Aircraft and Fuel

Fighters, Bombers and Nuclear units have domain 1. They pay three thirds per step on any terrain, ignore zones of control, and cannot enter a foreign city (*OCCUPY), except a Nuclear unit, which explodes there.

Fuel

utypes[type].fuel is the number of turns an aircraft may end away from a base: 1 for the Fighter and Nuclear unit, 2 for the Bomber. The unit’s own fuel byte counts down:

• create_unit() sets it to fuel - 1, and so does being carried by a moving Carrier.
• When the aircraft has used all its movement, ai_turn() refills it to fuel if the aircraft is in a city or with a Carrier, then subtracts one. A result below 0 destroys the aircraft (*FUEL).
• Ending a move in a city, or on a Carrier, stops the aircraft for the turn; on a Carrier it is also refuelled.

A Fighter therefore has to finish every turn at a base. A Bomber may spend one turn in the air between bases, and the AI sends it home ('h') when its fuel is spent. A Bomber’s movement ends after it attacks.

Returning to base

The human’s 'h' order on an aircraft away from a city calls near_base() in UNITS.C. It finds the nearest of the owner’s cities and Carriers by the larger of the two coordinate distances, then picks the neighbouring step that most reduces distance_twice() to it, avoiding foreign units and cities. While the order lasts the unit carries status 0x02. If no step helps, a computer aircraft is disbanded.

Carriers

A Carrier (type 23) has capacity 0 in utypes, but the movement code treats it specially: when it moves, aircraft in its stack move with it, with no limit except the ten-unit cap of stack walks. Aircraft carried this way are refuelled to fuel - 1. A Carrier destroyed at sea takes its aircraft with it.

Air combat

Only a Fighter may attack an aircraft outside a city. Defending aircraft and ships use defense * 8, without terrain or fortification. A city’s walls do not help an aircraft. See Combat.