The air unit intercept order range is equal to their attack range.
- Triplane: 5
- Fighter: 8
- Zero: 8
- Jet Fighter: 10
- Air unit "Range" promotion: +2
The intercept range of naval and ground units is 2. The automatically attempt to intercept if and only if they have movement left.
Intercept is a single preemptive strike against an attacking air unit. The attacker must be targeting a friendly unit or city in range (including the interceptor itself for land and naval interceptors).
Each unit's intercept ability has a percentage chance to hit. Only later tech interceptors have a 100% chance to hit.
If you do not deal enough damage to destroy the attacker in the intercept, combat will continue to resolve normally the targeted friendly unit, damaging both defender and attacker, potentially killing either.
Each intercepting unit can only intercept once per turn (before promotions), and only one interceptor will strike each attacker (even if multiple interceptors are in range). This means you can get use out of one defending interceptor per air attack, but extra are wasted.
Because a kill on preemptive strike can prevent all damage to the defending unit (including very weak units like those embarked), or at least cause the attacker to die in normal combat, powerful and reliable interceptors are very useful. Building or upgrading to late tech interceptors and choosing the interception promotion on air interceptors can help secure more intercept kills.
When conquering island cities with many defending air units, carriers loaded with a mix of air interceptors and bombardment specialists with a naval interceptor escort can be very effective. The naval interceptor provides free intercept capability, enemy submarine spotting, and naval melee unit for coastal city capturing. The fighters can intercept early air attacks, transitioning into air sweep, and finally bombardment when defending air units have been eliminated. The "Sortie" promotion for air interceptors allows you to get an additional intercept out of the same unit, giving you the opportunity to dedicate more units to air sweeps and bombardment.
Comparing this composition to a ranged naval unit plus embarked melee land unit army composition, there are obvious advantages in raw defensive combat strength, intercept ability, and submarine defense. But also carriers allow you to create tighter formations, getting more utility out of the limited intercept and submarine spotting range of your naval interceptor. Where ranged units have to spread into a ring around targets to focus fire, carrier groups can stay clustered while attacking.
Additionally, air units heal while their carrier moves, giving you a pseudo "March" promotion to your air units. Each individual air unit on a carrier can also attack before, after, or even between movements of the carrier, giving a pseudo "Blitz" promotion. Whereas ranged naval units would be spread out after attacking multiple widely spaced targets, your carrier group can continue to stay clustered. This helps your naval units from being picked off one by one by roving groups of enemy naval units, as well as keeping you in formation for city bombardment immediately after engaging targets of opportunity while traveling.