Anti-Aircraft

Anti-aircraft(AA) guns, sometimes known as anti-aircraft artillery(AAA) allow ships to shoot down enemy aircraft.

## AA Equipment

### Light AA

Light anti-aircraft (LAA) is unlocked by the "Heavy AA MG" technology in the Anti-Aircraft Artillery tree (base year 1918), and represents heavy machine guns of approximately 20mm calibre, such as the historical Oerlikon 20mm . Light AA weighs 1 ton and consumes 2 topside space per mount. Light AA may disrupt enemy planes that are preparing to attack, It may also damage/destroy enemy aircraft before they strike with the chance dependent on the speed of the attacking aircraft(otherwise it will damage/destroy the aircraft after it carried out its attack). Light AA only protects the ship that it is mounted on.

### Medium AA

Medium anti-aircraft (MAA) is unlocked by the "40mm automatic cannon" technology in the Anti-Aircraft Artillery tree (base year 1922), and represents very heavy machine guns of approximately 40mm calibre, such as the historical Bofors 40mm . Medium AA weighs 3 tons and consumes 3 topside space per mount, and it may disrupt or damage enemy planes before they attack. Medium AA only protects the ship that it is mounted on.

### Heavy AA

Heavy anti-aircraft (HAA) is initially unlocked by the "Dual purpose mounting" technology in the Turrets tree (base year 1917), and represents heavy anti-aircraft and dual-purpose mounts, such as the historical 5"/38 . The initial tech allows 3" and 4" guns to be dual-purpose (DP) mounts, and later technologies allow 5" and 6" DP guns. Heavy AA uses the same system of turrets as standard ship guns do, instead of consuming topside space directly. Heavy AA may damage and disrupt enemy planes before they attack, and it may be used to defend nearby ships as well as the ship that mounts the guns. To represent the difficulty of keeping track of different shell types, and to limit the potential effect of player designs with as many as 80 heavy AA guns, there is a -60% penalty to the effectiveness of all HAA mounts below the largest calibre on any given ship. *(Unclear whether AA directors, standard fire control directors, or both improve accuracy for HAA)*

### AA Directors

Anti-aircraft directors (AAD) are unlocked by the "Early AA director" technology in the Anti-Aircraft Artillery tree (base year 1926), and represent fire control systems used by AA mounts. A ship may mount up to 4 AA directors, and each weighs 15 tons. The first consumes 1 topside space, while any additional ones consume 3 each. AA directors improve the effectiveness of AA weapons.

## Topside Space

The primary limit on mounting AA guns is topside space. This reflects the amount of space available on a ship's upper deck, after all other equipment (turrets, surface torpedo  tubes, etc.) has been placed. Topside space increases with a ship's mass, but it may be used up quickly, especially on ships that mount large numbers of weapons.

Topside space is tracked from 1900, but it only becomes relevant when LAA or MAA is unlocked. Topside space provides a hard limit on the amount of LAA/MAA/AAD that may be mounted on a ship - LAA consumes 2 space per mount, while MAA and AAD each consume 3 space per mount.

Guns placed in casemates do not reduce topside space, so casemates may be used to increase the space available for LAA/MAA/AAD. However, guns in casemates may never be dual-purpose, so depending on the ship this could reduce overall AA effectiveness by reducing the number of DP mounts. Consolidating weapons into smaller numbers of mounts also increases remaining topside space - for example, a secondary battery of a dozen guns in six double turrets will consume substantially less space than a dozen guns in twelve single turrets.