Rule 18. AIR OPERATIONS

18. AIR OPERATIONS 18.1 BASING
18.2 STAGING
18.3 RANGE
18.4 EMPLOYMENT
18.5 OFFENSIVE AIR MISSIONS
18.52 COUNTERAIR
18.53 AIR SUPPLY
18.54 AIR TRANSPORT
18.55 GROUND SUPPORT
18.56 INTERCEPTION OF DEFENSIVE AIR SUPPORT
18.57 BOMBING OF ECONOMIC TARGETS
18.58 ASSISTING FRIENDLY NAVAL ACTIVITIES
18.59 SPOTTING
18.6 DEFENSIVE AIR MISSIONS
18.61 DEFENSIVE AIR SUPPORT
18.62 INTERCEPTION OF AIR ACTIVITIES BY DEFENDER
18.7 UNINVERTING AIR UNITS

18.1 BASING:
18.11 BASING LIMITS: Basing limits are always stated in terms of air factors. A hex capable of basing air units may base three AAS or NAS for each allowable air factor. Thus a hex which may base five air factors could base four air factors and three NAS, three air factors and six NAS, and so on, up to a maximum of 15 NAS.
18.12 Each city, port, airbase and artificial port may base five air factors (EXCEPTION: Each city, port, airbase and artificial port in a Pacific theater one-hex island or hex containing jungle or jungle/mountain may base only three air factors). A hex containing two cities or a city and an airbase may therefore base ten air factors; a hex containing two cities and an airbase may base 15 air factors (or, in Pacific theater one-hex islands and hexes containing jungle or jungle/mountain, six or nine air factors, respectively).
18.13 Each one-hex island, in either theater, may base one NAS, in addition to whatever air factors it may base. A hex containing a one-hex island with a city or airbase counter may thus base five (or, in Pacific theater one-hex islands or jungle or jungle/mountain hexes, three) air factors and one NAS; a one-hex island with a city and an airbase counter may base ten (or, in Pacific theater one-hex islands or jungle or jungle/mountain hexes, six) air factors and one NAS.

18.14 AIRBASES: Each major power is provided with airbase counters as follows: Germany: 4; Japan: 3; Britain: 3 (Europe), 1 (Pacific); Russia: 3 (Europe), 1 (Pacific); U.S.: 3 (Europe), 3 (Pacific); Italy, France: 2; China: 1. The number of airbase counters may be expanded by production (42.22E).
18.141 OPENING SETUP: Each major power except the U.S. and Britain (Pacific only) may place one airbase on the board in each theater during the opening setup of a Global War campaign game. Airbases may be placed at the start of a scenario as specified in that scenario. The U.S. may not place airbases in Europe until it is at war with Germany, and the U.S. and Britain may not place airbases in the Pacific until the game turn after they go to war with Japan or until the USJT level reaches 40.
18.142 AIRBASE PLACEMENT: Once play begins, major powers may place airbases on the mapboard as follows:
A. Airbases may be placed on the board only during the placing player’s movement, unit construction and redeployment phases. Major powers that may place two airbases in a turn may place both of them in the same phase or in different phases. Airbases may not be placed during the opponent’s turn.
B. Each turn:

Italy, Japan, Britain, France and China may place one airbase.
Germany and the U.S. may place two airbases.
Russia may place one airbase each turn from 1935-1942; and may place two airbases each turn starting in Spring 1943.

In classic A World at War, Russia may place one airbase each turn from 1939-1942, and may place two airbases each turn starting in Spring 1943.
The airbase placement capabilities of Russia, Britain and the U.S. apply separately to each theater.

C. Airbases may be placed in any fully supplied hex, including hexes in the ZoC of enemy armor, controlled by the placing major power or an alliance faction partner, if permitted by the ally. A major power may not place an airbase in a hex controlled by an ally who is not a member of its alliance faction.

Airbases may not be placed in minor countries in the movement phase of the first turn of activation, association or hex control, as full supply would not yet have been traced to the minor country's hexes. The Western Allies may not place airbases in Russian-controlled hexes, and vice versa.

D. No more than one airbase counter may occupy a single hex.
E. No more than one airbase may be placed in each Pacific island group by each alliance faction (EXCEPTION: Airbases may not be placed in Aleutian islands).
18.143 RECYCLING AIRBASE COUNTERS: Once all of a nation’s available airbase counters are on the board, a player may only place an additional airbase counter by simultaneously removing an existing airbase counter from another hex, so that the total number on the board does not exceed the limit set out in 18.14. An air unit may stage or redeploy to a newly placed airbase which is created by recycling an airbase counter. If an airbase on which air units are based is recycled, those air units must stage or redeploy during that phase, including to the newly placed airbase.
18.144 Once placed, airbase counters may not be moved or redeployed. This prohibition does not prevent the recycling of airbases to different hexes (18.143).
18.145 In a Global War game, the number of airbases, including airbases added by production (42.22E), and the recycling capacity of the U.S., Britain and Russia are distinct for each theater.
18.146 Only air units belonging to the placing major power may use an airbase in the phase in which it is placed (EXCEPTION: Australian and Free French air units may use British airbases in the phase in which they are placed). In subsequent phases of the turn of placement, air units belonging to the placing major power’s major power allies, minor allies and associated minor countries may use the airbase. Thus a German air unit may redeploy to an Italian airbase placed during the movement or unit construction phase, but may not redeploy to an Italian airbase placed during the redeployment phase of that player turn. This restriction does not prevent a major power from placing an airbase in a hex containing a city during the movement phase and staging an air unit to that airbase, while an ally stages an air unit to the city.
18.147 An airbase is removed from the board if the hex it occupies comes under enemy control. Airbases which are cut off from supply by enemy action are removed from the board in the same manner as ground units. In either case, the airbases may be placed on the board again in accordance with 18.142.
18.15 If the recycling or removal of an airbase, or the failed or aborted sea transport of air units, results in there being more air units in a hex than the basing capacity of that hex, the excess air factors must be moved or redeployed to another base or mapboard box in the same phase or be eliminated. When an airbase is overrun or eliminated by isolation or surrender, the provisions of 18.25 apply.

18.2 STAGING:
18.21 An air unit may stage (change base) up to twice its operational range at the beginning of the movement phase whether or not it is inverted, subject to the following:
A. The new base need not be on the same front as the old base.
B. The new base must have been controlled by the staging side at the start of its movement phase. Air units may not stage to new bases acquired by ground units during the same movement phase.
C. Association by an attacked minor country or a successful diplomatic die roll resulting in hex control of a minor country results in the acquisition of air bases which may be used immediately.
D. An air unit may stage to a base which is not fully supplied, but it may not carry out any activities from the new base unless supply is later provided to it (30.523). An air unit may stage to a base which is partially supplied (30.523A) or subject to air oil effects, but may only conduct defensive air activities and only over the hex in which it is based.
18.22 Staging may not be intercepted. Air units may stage over all playable non-neutral territory, including enemy-controlled territory, territory of minor countries independently at war and hexes controlled by no one. Air units may not stage over land hexes that are completely neutral, but may stage over hexes which are part water, part neutral land, provided they do not cross a hexside containing exclusively neutral land.
18.23 Western Allied air units may stage off the mapboard to the Australia and India boxes (5.57A, 5.47A) and Russian air units may stage off the mapboard to the Urals box (5.77A). Air units may not otherwise stage off the mapboard.
18.24 Air units may be sea transported from one port to another during the movement phase. Air units may not stage during a turn in which they are sea transported. The destination port becomes the air unit’s new base. Air missions may be flown from the new base, subject to supply requirements.
18.25 DISPLACED AIR UNITS: Air units on bases that are occupied by enemy units or on airbases that are eliminated by isolation are displaced to the nearest controlled base within staging distance that has the capacity to base them, regardless of its supply status. Should two such bases be equidistant, the owning player chooses. If the nearest base is able to base only some of the displaced air units, the owning player chooses which air units go to that base, and the remainder go to the next closest base. Air units which are unable to reach a base within range with the capacity to base them are eliminated. If a base is captured while its air units are absent on a defensive air mission, any air units which attempt to return to the captured base are displaced at the end of the phase in which they flew their mission. Mapboard boxes are considered bases for the purpose of this rule and may receive displaced air units.
18.251 If an enemy airborne unit airdrops on a hex that is defended by a ground unit, any air units based in that hex are displaced from their base only if the enemy airborne unit wins the resulting ground combat.
18.252 The movement of displaced air units may not be intercepted.
18.253 EFFECT OF DISPLACEMENT: Displaced air units are inverted.

18.3 RANGE:
18.31 RANGE: Air units have the following ranges:
A. ARMY AIR UNITS: Four hexes in Europe and three hexes in the Pacific.
B. NAVAL AIR UNITS: Three hexes in both Europe and the Pacific, whether operating from land or from carriers.
C. KAMIKAZES: Four hexes.
D. AIR TRANSPORT UNITS: Four hexes in Europe and three hexes in the Pacific.
E. JETS: Two hexes in Europe and one hex in the Pacific after a research result for jets of “9”; three hexes in Europe and two hexes in the Pacific after a research result for jets of “11”; four hexes in Europe and three hexes in the Pacific after a research result for jets of “12+”.
F. STRATEGIC BOMBERS: The minimum range of strategic bombers is four hexes in Europe and three hexes in the Pacific. This may be increased by air range research (17.72).
G. INTERCEPTORS: Interceptors operating defensively in an SW box may engage enemy strategic bombers only if the strategic bombers pass through or attack targets on the interceptor's assigned front and pass within interceptor range of any controlled, fully-supplied air base on their assigned front, regardless of the number of other air factors using the base. Interceptors may also escort strategic bombers to their targets, subject to their range as determined by their current air range research result (17.82).

18.4 EMPLOYMENT:
18.41 ONE MISSION PER PLAYER TURN: During each player turn uninverted air units may perform one, and only one, offensive or defensive air mission; or may search, provide air cover, or attack enemy naval units at sea with respect to one or more naval activities during the same player turn, as set out in 23.16. An air unit may perform an offensive mission during its player turn and a defensive mission during the opposing player turn, provided it is uninverted when it performs each mission.
18.42 INVERSION OF AIR UNITS:
A. Air units which perform an air mission are inverted for the remainder of the player turn. Air units are uninverted at the end of the player turn as set out in 18.7.
B. Air squadrons which search, provide air cover or attack enemy naval units at sea are not considered to be flying a mission and may be used for these purposes in more than one phase, but may not perform air missions in the turn they do so. Air squadrons used for these purposes in the movement and combat phases are inverted at the start of the redeployment phase if redeployed, or at the end of the redeployment phase if not redeployed (23.164). For the inversion of AAF formed by combining AAS, see 23.144.
C. Air units which assist in naval interception by spotting enemy naval units are not considered to be flying a mission and are not inverted (22.22F).
18.43 EFFECTS OF COUNTERAIR: Air units that are counteraired and either forced to abort during the final round of air combat or disengage from air combat by leaving their base are inverted and may not perform any mission for the remainder of the player turn.
18.44 For naval air units on carriers, see 21.55.
18.45 OPERATIONAL RANGE: An air unit may fly a number of hexes from its base equal to its range to perform offensive air missions during the movement or combat phase, either during an offensive option, as a limited offensive operation, or by participating in an alliance faction partner’s offensive option. This operational range is in addition to staging. An air unit may stage up to twice its range during the movement phase, then fly to a target hex during the combat phase, then return to base (EXCEPTION: Kamikazes do not return to base). A defender’s air unit may also fly a number of hexes from its base equal to its range to perform defensive tasks (EXCEPTIONS: Air units subject to a winter result of "9" or air oil effects, or which are based in a partially supplied base (30.523A), may only fly defensive air operations over the hex in which they are based).
18.46 RETURNING TO BASE: Subject to stacking limits, land-based air units which survive an air activity may return to their base of origin or any operational base within range of their activity hex that was under friendly control at the start of the phase in which the air activity was conducted. Air units that return to a base other than their base of origin are immediately inverted.
18.47 AIR INTERACTIONS:
18.471 During each phase of the attacker's turn, the possibility arises that defending air may intercept an air transport activity (18.62) or participate in a naval activity (18.63).
18.472 The attacker may use eligible air units to counter-intercept the defender's interception of air transport activities (18.622). This is considered to be an offensive operation and the attacker must pay the normal BRP cost to employ his air units in this manner. Once the resulting air combat is resolved, the surviving air units for both sides are inverted for the remainder of the player turn.
18.473 The attacker and defender may also use eligible air units to search, provide air cover, or attack enemy naval units at sea (22.4422, 23.2, 23.7). Neither player has to pay any BRPs to use his air units in this manner. Air units which survive these activities and any air combat arising out of them are inverted at the end of the redeployment phase of the player turn in which the activity took place.
18.48 The restrictions of 18.22 governing the movement of air units over neutral hexes also apply to air units which fly offensive and defensive missions or redeploy.
18.49 Air missions may not be flown within a mapboard box, from the mapboard into a mapboard box, or from a mapboard box onto the mapboard except as follows:
A. Axis air units may bomb the Atlantic U.S. box, if the Axis have achieved three air range research results, or the Urals box (26.31, 26.462).
B. Japanese air units may bomb the Australia box, the India box, the Pacific U.S. box, if Japan has achieved three air range research results, or the Urals box (26.31, 26.462).
C. During Murmansk convoy battles (40.45).

18.5 OFFENSIVE AIR MISSIONS:

18.51 ELIGIBLE BASES: Offensive air missions may only be flown from fully supplied cities or airbases, or (NAS only) one-hex islands or carriers. Offensive air missions may not be flown from partially supplied bases (30.523A) or bases which are subject to air oil effects. The same restriction applies to the use of air units to search, provide air cover, or attack enemy naval units at sea.
18.511 AIR MISSIONS DURING THE MOVEMENT PHASE: The following offensive air missions may be flown during the movement phase:
A. Counterair (18.52).
B. Attacks on patrolling submarines (21.4184C).
C. Attacks on bases by patrolling TFs (21.41, 23.6).
D. Air supply (18.53).
E. BRP grants to China over the Hump (using air transports at no BRP cost - 40.85).
F. Air transport (18.54).
G. Ground support for overruns (18.55).
H. Interception of defensive air support for overruns (18.56).
I. Counter-interception of defending air which intercept air transports (18.622).
18.512 AIR MISSIONS DURING THE COMBAT PHASE: The following offensive air missions may be flown during the combat phase:
A. Counterair (18.52).
B. Attacks on naval bases (23.5, 23.6).
C. Airdrops (10.53).
D. Ground support, both for regular and exploitation attacks (18.55).
E. Interception of defensive air support (18.56).
F. Strategic bombing (26).
G. BRP grants to China over the Hump (using air transports at no BRP cost - 40.85).
H. Counter-interception of defending air which intercept air transports (18.622).
18.513 AIR MISSIONS DURING THE REDEPLOYMENT PHASE: The following offensive air missions may be flown during the redeployment phase at no BRP cost:
A. Air transport (18.54).
B. Counter-interception of defending air which intercept air transports (18.622).

18.52 COUNTERAIR:
18.521 Land-based air units and carrier-based air units at sea (17.33A) may counterair any enemy air base within range.
A. If the counteraired air base contains air units, the attacking air units must engage in at least one round of air combat with the defending air units.
B. All defending air units in the attacked air base engage the attacker, whether or not they are inverted. Air transport units may be engaged by the attacker, but are not counted when determining the air combat strength of the defender.
C. Carrier-based naval air units concealed by a TF marker are revealed when the attacker announces his counterair attack on their base and must participate in counterair combat.
D. Counterair attacks may be made against enemy air bases which do not contain air units.

Two examples of counterair attacks against enemy air bases which do not contain air units come to mind. The first is a counterair attack against an empty air base to deny the air base as a refuge to enemy air units withdrawing from another counterair attack (18.523). The second is a counterair attack against an enemy port containing a TF to determine whether the TF contains carriers carrying NAS (17.3123, 20.164A).

18.522 After one round of counterair combat is resolved:
A. If either the attacker or defender had all its air units eliminated, the counterair combat ends.
B. If both sides had air units survive, each side has the option of disengaging from the air battle:

The defender announces his decision to disengage first. If he disengages, the counterair combat ends.
If the defender elects to continue the counterair battle with his surviving air units, the attacker has two options:
- The attacker may disengage, ending the counterair combat.
- The attacker may initiate a second round of counterair combat with his surviving air units, including those forced to abort by the defender’s previous counterair combat dice roll. The attacker may reinforce his surviving counterairing air units with additional, previously uncommitted air units.

C. This continues until one side or the other disengages or is completely eliminated.
18.523 The defender disengages from counterair combat by flying all surviving defending air units, including naval air units based on carriers in port, to one or more controlled air bases or mapboard boxes within staging range with the capacity to base them which are not also being counteraired, and which have not been counteraired earlier in the same phase. If no such bases exist, the defender may not disengage from counterair combat. Partial disengagement is not permitted. If the defender disengages from counterair combat, all surviving defending air factors are inverted for the remainder of the player turn.
18.524 Regardless of the outcome, once all rounds of counterair during the current phase are resolved:
A. LAND-BASED AIR: All surviving attacking land-based air units return to base (18.46) and are inverted for the remainder of the player turn.
B. CARRIER-BASED AIR: All surviving attacking carrier-based air units return to their carriers and, if their carriers are engaged in naval combat, are inverted for the remainder of that round of naval combat. Once any naval combat in which they are involved is resolved, they return to base with their carriers.
18.525 A defending air unit may be counteraired by different attacking air units during the movement and combat phases.
18.526 EFFECTS OF COUNTERAIR ATTACKS ON SURVIVING DEFENDING AIR UNITS: If the defender does not disengage from counterair combat, the status of the defender's surviving air units is determined by the attacker's final air combat dice roll:
A. Defending land-based air units which were forced to abort by the attacker's final counterair combat dice roll (the number after the "/" on the Air Combat Table result) are inverted for the remainder of the player turn. Excess abort results are disregarded. See 22.43 for the effects of counterair attacks during naval combat.
B. Naval air units, including NAS forced to abort by the attacker's final counterair combat dice roll, may return to their carriers if they go to sea, adopting the inversion status of their carriers (17.3126C).
C. Defending air units which were not forced to abort by the attacker's final counterair combat dice roll may operate without impairment during the attacker's player turn.
18.527 AIR SURPRISED ON THE GROUND AT PEARL HARBOR: For the effects of surprise on air units at Pearl Harbor, see 51.36.

18.53 AIR SUPPLY:
18.531 TIMING: Air supply missions may be flown by air transport units only during the movement phase, after the tracing of sea and land supply lines. Air transport units providing air supply must operate from fully supplied bases.
18.532 AIR TRANSPORTS REQUIRED: Each uninverted air transport factor may provide limited supply to one ground unit. The total number of ground units which may be air supplied each turn is limited by the number of available air transport units. Units may receive air supply from an alliance faction partner's air transport units if not prohibited from doing so by cooperation restrictions (53).
18.533 BASING AND SUPPLY: Air transports providing air supply must fly from a fully supplied city or airbase not subject to air oil effects to ground units within their operational range.
18.534 AIR SUPPLY SUBJECT TO INTERCEPTION: Air transports flying air supply missions may be intercepted by eligible defending air units (18.62).

18.54 AIR TRANSPORT:
18.541 TIMING: During the movement phase, at the same time as sea transport (21.43), or during the redeployment phase (28.36), eligible ground units may be air transported up to eight (Europe) or six (Pacific) hexes.
18.542 AIR TRANSPORTS REQUIRED: Each uninverted air transport factor may air transport one ground unit. The total number of ground units which may be air transported each turn is limited by the number of available air transport units. Units may be air transported by an alliance faction partner's air transport units if not prohibited from doing so by cooperation restrictions (53).
18.543 ELIGIBLE UNITS: Each uninverted air transport factor may air transport a one-factor infantry unit or a specialized unit.
18.544 PROHIBITED UNITS: Armor units, two- and three-factor infantry units, replacements, partisans and other units may not be air transported.
18.545 BASING AND SUPPLY: Air transport must begin and end in a city or airbase. Both air bases must be operational. The air transport factor involved may stage to the city or airbase from which the air transport activity is flown and may end the movement phase in either air base used in the air transport mission.
18.546 AIR TRANSPORT SUBJECT TO INTERCEPTION: Air transports flying air transport missions may be intercepted by eligible defending air units (18.62).
18.547 GROUND UNITS:
A. MOVEMENT: Ground units may use their full movement capability during the player turn in which they are air transported. Ground units may move to their base of embarkation before being air transported, prior to the movement of other ground units. Only ground units which have sufficient movement factors to meet the costs of embarkation (if any) and debarkation may be air transported. Ground units may move after being air transported, if permitted by their remaining movement factors, and may engage in offensive ground attacks or attrition in conjunction with other ground units.

There is no movement cost to embark (EXCEPTION: If the port of embarkation is in an enemy ZoC, there is a movement cost of two movement factors in Europe and one movement factor in the Pacific to embark, even if the ground unit and the air transport factor begin the turn in the base of embarkation).
There is a movement cost of one movement factor to debark, plus an additional movement factor if the base of debarkation contains rough terrain (EXCEPTIONS: Japanese ground units and the Chindit entering jungle hexes do not incur an additional movement cost - 13.41C). There is no additional movement cost to debark in a hex in an enemy ZoC.

B. STACKING: The number of ground units which may air transport from or to a single base is not limited by stacking limits.
C. RESTRICTIONS:

Ground units which are unsupplied may not be air transported.
A unit may not be air transported from one location to another, then air transported again from the new location, in the same turn.
A ground unit may not be air transported and sea transported in the same movement phase.
Ground units which are air transported may not airdrop or invade in the same turn.

18.55 GROUND SUPPORT:
18.551 Air units within range of a hex capable of being attacked by ground units may fly to that hex and add their combat factor to that of any attacking ground units. Overruns and exploitation attacks may be similarly supported by air units. Air units which provide ground support during exploitation may not have provided ground support during the regular combat phase, even against the same hex. If a ground attack against more than one enemy hex is being conducted, the attacker may add ground support to his attack if his air units are able to reach all of the attacked hexes.
18.552 GROUND SUPPORT FROM NAVAL AIR UNITS: Naval air units, whether land-based or carrier-based, may provide ground support.
18.5521 Three NAS provide one factor of ground support, six NAS provide two factors of ground support, and so on. If ground combat losses are taken from naval air units, the 3:1 ratio is also used. Ground support from naval air units may be used in conjunction with shore bombardment, with remnants from both being added together.
EXAMPLE: Five infantry factors, supported by 12 NAS, invade a one-hex island defended by a 1-2 infantry unit. The ground combat ratio is 9:3 = 3:1. The attacker rolls a "1", and an exchange results. If the attacker wished to preserve his invading units, he would have to remove nine NAS.
Five NAS and seven fleet factors provide ground support and shore bombardment for an invasion. The total increase in attacking strength is four factors.
18.5522 GROUND SUPPORT FROM FAST CARRIERS: Carrier-based naval air units may provide ground support for regular ground attacks, including seaborne invasions, but not for exploitation attacks, provided the carriers are at sea within air range of the attacked units.
18.553 GROUND SUPPORT FROM CVEs:
A. CVEs may provide ground support only for seaborne invasions. CVEs which provide ground support must be in the invasion hex.
B. Each CVE factor which provides ground support adds one factor to the ground attack.
C. The number of combat factors added to a ground attack by ground support from CVEs may not exceed the number of invading ground factors involved in the invasion attack.
D. CVEs which provide ground support count against the overall limit on ground support. Ground support from CVEs may be supplemented by additional ground support from AAF or NAS, up to three times the number of invading ground factors involved in the invasion attack.
E. CVEs which provide ground support may be eliminated as a result of ground combat in the same manner as fleets providing shore bombardment (21.52). The attacker may freely choose from among participating ground, air and naval units when satisfying ground combat loss requirements, subject to 18.556 and 21.517H.
18.554 LIMITS ON GROUND SUPPORT:
A. LIMIT: The total number of AAF or their naval air equivalent and CVEs which may provide ground support for an attack may not exceed three times the total number of attacking ground factors.
B. CVEs: In addition to this overall limit, ground support from CVEs is limited to the number of invading attacking ground factors (18.553C).
C. LIMIT APPLIES ONLY AT THE START OF COMBAT: Once placed, ground support is not affected by the loss of ground units in combat - the limit on the amount of ground support applies only at the start of combat.
18.555 ELIMINATION OF GROUND SUPPORT IF ATTACK NOT MADE: If the attacking player decides not to attack a hex to which ground support has been committed, the air units providing ground support are eliminated. Air units providing ground support are not eliminated when the attacker is unable to attack as a result of enemy action or aborts a naval mission, but a voluntary decision not to attack, or a decision to attack with fewer ground factors than required to comply with 18.554, results in the elimination of the excess air units providing ground support.
18.5551 Ground support may be provided for seaborne invasions. If an invasion is turned back by the enemy, or is voluntarily aborted by the attacking player, air units providing ground support are not eliminated. The air units return to base and are inverted for the remainder of the player turn.
18.5552 If the interception of a portion of an invasion force or the sea transport of ground units results in more ground support than is allowed (18.554), the excess air factors are not eliminated. The excess air factors return to base and are inverted for the remainder of the player turn.
18.556 AIR LOSSES FROM GROUND COMBAT: If the attacker suffers ground combat losses, some, all or none of these losses may be taken from air units that provided ground support, provided sufficient factors are eliminated.

18.56 INTERCEPTION OF DEFENSIVE AIR SUPPORT:
18.561 After the defender has committed his air units to defensive air support (18.61), the attacker may intercept such defensive air support with any uninverted air units within range of the hex in which the defensive air support has been placed. Defensive air support provided in connection with overruns and exploitation attacks may also be intercepted.
18.562 AIR INTERCEPTION FROM CARRIERS: Naval air units based on fast carriers at sea may intercept defensive air support provided the carriers are within air range of the hex in which the defensive air support has been placed. Carrier-based and land-based air units may combine to intercept the same defensive air support. CVEs may not intercept defensive air support (20.42).
18.563 RESOLVING INTERCEPTION OF DEFENSIVE AIR SUPPORT:
18.5631 When defensive air support is intercepted, at least one round of air combat between the intercepting and defending air units is resolved. The defender then has the option of returning to base or continuing his defensive air support mission.
18.5632 If the defending air units which survived the initial round of air combat elect to return to base, their defensive air support mission is canceled and no additional rounds of air combat take place.
18.5633 If the defending air units which survived the initial round of air combat elect to continue their defensive air support mission, all defending air factors which were neither eliminated nor forced to abort by the attacker’s final air combat dice roll (the number after the “/” on the Air Combat Table) provide defensive air support (subject to 18.614), unless the attacker elects to fight another round of air combat.
18.5634 If the defender elects to continue his defensive air support, the attacker may initiate a second round of air combat with his surviving air units, including those forced to abort by the defender's previous air combat dice roll; may reinforce his interception with additional, previously uncommitted air units, whether or not any intercepting air units survived the previous round of air combat; or disengage. All air units flying defensive air support which were not eliminated in previous rounds of air combat must be engaged, including those which were forced to abort in the previous air combat round. This continues until one side or the other disengages or is completely eliminated.
18.564 All surviving intercepting air factors return to their base and are inverted for the remainder of the player turn after the resolution of air combat with the defending air factors, regardless of the outcome.

18.57 BOMBING OF ECONOMIC TARGETS: See rule 26.

18.58 INTERACTING WITH NAVAL ACTIVITIES: Uninverted AAS or NAS in an operational air base may interact with naval units at sea as set out below. The use of air units in this manner is not an offensive mission and does not require the expenditure of BRPs. Searching, providing air cover and attacking enemy naval units at sea causes the air units used to be inverted at the end of the redeployment phase of the player turn in which they carry out the activity.
A. Searching (search AAS and land-based NAS - 22.4422).
B. Providing air cover (cover AAS and land-based NAS - 23.2).
C. Attacking enemy naval units at sea (attack AAS and NAS - 23.7).
18.59 SPOTTING: Uninverted search AAS or NAS in an operational base may assist naval interceptions (22.22F). Spotting does not invert the search AAS or NAS involved. Air units that spot may be used for another activity later in the turn, but air units already committed to another activity may not spot later in the turn.

18.6 DEFENSIVE AIR MISSIONS:

18.61 DEFENSIVE AIR SUPPORT:
18.611 During an enemy player turn, in the movement phase when overruns are attempted and in the combat phase, after the attacker has announced his ground support air missions, uninverted defending army air units and land-based naval air units may provide defensive air support to any ground units within range which are being overrun or that the defender thinks may be subject to ground attack, including by seaborne invasion and as yet unannounced airdrops (EXCEPTION: Defensive air support against low-odds attacks is deferred - 18.619).
A. EFFECT: Air units which fly defensive air support increase the strength of the defending ground units. The effect of defensive air support is not affected by the DM of the defending ground units. The defender has the option of not using all, some or none of his defensive air support prior to the resolution of regular ground combat to preserve defensive air support for possible exploitation combat (18.618).
B. GROUND ATTACKS: Each AAF, and every three NAS, which fly defensive air support adds one factor to the strength of ground units defending against non-invasion ground attacks.
C. INVASION ATTACKS: Each AAF which flies defensive air support adds three factors to the strength of ground units defending against seaborne invasion; each NAS which flies defensive air support adds one factor to the strength of ground units defending against seaborne invasion. The number of factors added to the strength of the ground units is used when determining losses (15.63).
D. RESTRICTIONS: Defensive air support is subject to the following restrictions:

Air units in a partially supplied base (30.523A), subject to air oil effects (33.61A) or providing defensive air support to units in a hex subject to a winter result of "9" may only fly defensive air support over the hex in which they are based.
Defensive air support may be prohibited by cooperation restrictions (53.251D, 52.42, 53.52).
Defensive air support may not be provided to partisans. If partisans and non-partisan ground units are attacked together, the non-partisan ground units may receive defensive air support (11.47).

18.612 Land-based naval air units may provide defensive air support; carrier-based naval air units may not. Three NAS (round down) are required to provide one factor of defensive air support (EXCEPTION: Each NAS provides one factor of defensive air support against seaborne invasions - 18.611C).
18.613 The defender may similarly commit army air units which have not yet flown during that game turn to defensive air support of units being subject to overruns, or during exploitation. Defensive air support placed during movement that prevents an overrun remains in its hex and provides defensive air support during regular combat; defensive air support placed during regular combat may remain in its hex to provide defensive air support against exploitation attack, at the defender’s option, provided it was not eliminated or forced to abort in air combat with intercepting attacking air units and was not used in regular ground combat.
18.614 LIMITS ON DEFENSIVE AIR SUPPORT:
A. 3:1 LIMIT: The number of AAF or their naval air equivalent which fly defensive air support may not exceed three times the number of defending ground factors. DMs are ignored when making this determination.
B. LIMIT APPLIES ONLY AT THE START OF COMBAT: Once placed, defensive air support is not affected by the loss of ground units in combat - the limit on the amount of defensive air support applies only at the start of combat.
C. EXCESS AIR: A player may commit additional air units in excess of the 3:1 limit on defensive air support, in anticipation of enemy interception and air combat, but the number of air factors which actually provide defensive air support when ground combat is resolved may not exceed the 3:1 limit. Such additional air factors:

May not participate in any rounds of ground combat, even if ground combat losses cause the number of air factors providing defensive air support to drop below the 3:1 limit.
Are unaffected by the results of the ground combat.
Are considered to have flown a defensive air mission and are inverted for the remainder of the player turn when they return to base.

18.6141 JET ESCORT OF DEFENSIVE AIR SUPPORT: Jets may escort army and naval air units flying defensive air support. Jets are not included when determining the 3:1 limit on defensive air support, are unaffected by the results of ground combat, and are considered to have flown a defensive air mission and are inverted for the remainder of the player turn when they return to base. Army and naval air units may not escort defensive air support and are always subject to possible elimination as a result of ground combat unless they exceed the 3:1 limit on defensive air support.
18.615 If the attacker commits ground support and the defender commits defensive air support to the same ground battle, there is no direct air interaction. Each side simply adds its air factors to those of its ground units.
18.616 Air units which provide defensive air support may be eliminated by adverse results in ground combat. Should a combat result leave the defender with surviving factors, he may elect to take his losses from either air or ground units or both, in any combination, provided he eliminates sufficient factors (subject to 15.632).
18.617 Defending air units which do not fly defensive air support may not be eliminated by an adverse ground combat result. An air unit which is based in an attacked hex and has not been committed to defensive air support does not take part in the ground combat and is simply displaced (18.25) if attacking ground units advance into the hex after combat.
18.618 Air units committed to defensive air support during the regular combat phase may remain in their hex to provide defensive air support against exploitation attacks, at the defender’s option, provided they were not eliminated or forced to abort in air combat with intercepting attacking air units and were not used in regular ground combat. Air units that provided defensive air support have performed a mission and are inverted for the remainder of the player turn even if the attacker does not attack the ground units they were supporting.
18.619 DEFERRED DEFENSIVE AIR SUPPORT AGAINST LOW-ODDS ATTACKS: When the attacker announces a ground attack with initial odds of less than 1:1, the defender may use eligible, uncommitted air units to provide defensive air support to the attacked unit(s). Deferred defensive air support may be intercepted by the attacker in the normal manner. The ensuing air combat does not affect any previously provided defensive air support. Regardless of the outcome of any air combat between the attacker’s intercepting air units and the deferred defensive air support, the attacker must complete the ground attack, even at worse odds. This sequence is repeated throughout the attacker’s player turn, provided the defender has air units eligible to provide deferred defensive air support.

18.62 INTERCEPTION OF AIR ACTIVITIES BY DEFENDER:
18.621 INTERCEPTION: The defender may use uninverted air factors in an operational air base to intercept any of the following attacker air transport activities in any one hex along the air transport's route, including the base of origin and the destination hex:
A. Air supply.
B. Air transport.
C. Airdrops.
D. BRP grants to China flown over the Hump.
18.622 COUNTER-INTERCEPTION: If an air transport activity is intercepted, eligible friendly air units may attempt to protect the air transport activity by counter-intercepting the intercepting defending air units in the same manner as defensive air support is intercepted (18.56). All counter-intercepting air units engage in air combat with all intercepting air units. One round of air combat is then resolved. The intercepting player then may elect to engage in additional rounds of air combat with his surviving intercepting air units. If he does so, the moving player may reinforce his counter-intercepting air units with additional, previously uncommitted air units, whether or not any counter-intercepting air units survived the previous round of air combat. A second round of air combat is then resolved. This process continues until one side or the other withdraws or is eliminated. Excess defender air combat effects have no effect on the air transport itself.
18.623 ATTACKS BY SURVIVING INTERCEPTING AIR UNITS OPTIONAL: Once air combat between the intercepting and counter-intercepting air is resolved, some, all or none of the intercepting air units may attack the air transport by making a single air combat dice roll. Intercepting air units which were eliminated or forced to abort by the result in the final round of counter-interception air combat may not attack the air transport. No air combat dice roll is made by the air transport. If the air transport is eliminated or forced to abort, the air transport activity fails. Intercepting air units which did not engage in air combat with counter-intercepting air units and which do not attack the air transport return to base, are not inverted and may be used later in that player turn.
18.624 EFFECT ON GROUND UNITS: Grounds units being air transported or air dropped return to base if their air transport is forced to abort and are eliminated if their air transport is eliminated by the defender's air combat result.

18.63 ASSISTING FRIENDLY NAVAL ACTIVITIES: The defender may use uninverted AAS or NAS in an operational air base to assist friendly naval units at sea in same manner as the attacker (18.58).

18.7 UNINVERTING AIR UNITS:
18.71 An alliance faction may uninvert all its land-based air factors at any time during its player turn, subject to the restrictions in 18.72.
RESTRICTIONS: The uninversion of air units is subject to the following restrictions:
A. FULL SUPPLY REQUIRED: Air units may only be uninverted if they are fully supplied.
B. UNINVERSION AFTER USE ONLY AT END OF PLAYER TURN: When the rules state that an air unit is "inverted until the end of the player turn", this means that the air unit may not be uninverted until the final part of the player turn, after the redeployment phase. Air units which engage in an activity which results in inversion may therefore not be used again until the opposing player turn. Air units may be uninverted at the start of the owning player's turn and again at the end of the friendly player turn, after use; then may be used during the opposing player turn.

There are a number of examples of this general rule. For example, air units which carry out operations during their player turn (18.42) and naval air units flying combat air patrol which land on air bases rather than carriers (22.463B), are inverted until the end of their player turn, at which point they may be uninverted and used during the ensuing opposing player turn - provided they are not redeployed (28.81).

C. NEW CONSTRUCTION: Air units may not be uninverted until after the redeployment phase of the player turn in which they are constructed. If redeployed to a new base during the redeployment phase, they remain inverted through the following opposing player turn (27.82A).
D. REDEPLOYMENT:

Inverted air units which redeploy to a new base during the redeployment phase may not be uninverted at the end of the player turn of use (EXCEPTION: American air units may be uninverted if redeployed in a theater in which the U.S. is not yet at war).
Air units which are TRed, then used to assist NRs, may not be uninverted until the next player turn.

E. OPPOSING PLAYER TURN: Air units may not be uninverted during the opposing player turn.
18.73 AUTOMATIC UNINVERSION: Air units in the following locations are uninverted at the end of the owning player's turn, even if out of supply:
A. STRATEGIC BOMBERS AND INTERCEPTORS: All strategic bombers and interceptors in an SW box.
B. WESTERN ALLIED AIR UNITS: All Western Allied air units in the U.S. boxes, unless NRed into the U.S. box during the current player turn.