Which item is prohibited from being stowed in a small arms locker?

The correct choice is that 20 MM CIWS rounds are prohibited from being stowed in a small arms locker due to their classification and safety regulations surrounding larger munitions. Small arms lockers are specifically designed for storing small arms ammunition, which typically includes ammunition for weapons like handguns and rifles, such as 9 MM ammunition. In contrast, 20 MM CIWS (Close-In Weapons System) rounds are classified as larger caliber munitions used in more extensive naval weapon systems and require specific storage considerations due to their complexity and the potential hazards associated with them.

Hand grenades are also generally stored separately in designated explosive storage areas, as they are classified as explosive ordnance rather than small arms ammunition. Rifle cleaning supplies, on the other hand, are not munitions and thus do not have restrictions related to explosive safety, making them suitable for storage within a small arms locker. The focus on the type of ammunition and ordnance plays a crucial role in ensuring compliance with safety regulations and proper handling procedures on an aircraft carrier.