A hybrid armored component and modular armor.
A Weapon Bay Door can be installed in the same location as any weapon system. It weighs half a ton, and takes up 1 critical slot. If the weapon is split across two locations, it instead weighs 1 ton and takes up 1 slot in each location.
Brackets are added to the record sheet surrounding the Bay Door slot and the slots of any weapons it protects. Then, for each critical slot of weapon that is so protected, add 1 extra pip of armor, and mark off those bonus pips with a hatched line. (This is applied to the front of any torso location, unless the weapon is rear facing.)
For instance, a Catapult with an LRM 15 protected by a bay door would spend 0.5 tons and 1 slot in the same arm. Three armor pips would be added to that arm.
If the location is struck with a through-armor crit and a critical hit would be applied to protected weapon, instead the bay door is crit. When the bay door is crit, immediately mark off any remaining armor pips the bay door provided.
However, if an attack's damage grouping destroys the last of the bay door armor pips and then deals internal damage, if the critical chance roll results in a critical hit, the first crit inflicted will be to the first undamaged slot of the protected weapons.
This can also be used to represent the clamping claws that protect a King Crab's AC/20s, or the bad doors on an Archer.