im pretty sure the small arms on board, regardless of any other theoretical need, are primarily stored and compartmentalized for the purposes of stopping a mutiny from taking control of critical areas and sealing off groups in non-essential areas through strategic control of access hatches/doors/etc. every ship constantly drills "general quarters" (action stations etc) which is a total lockdown in place where movement is tightly controlled, ostensibly an announcement of potential external threats. but it achieves a completely different purpose simultaneously.

the birth of every professional navy on earth was of kidnapping/pressganging men into servitude under threat of starvation, torture and death at sea for even minor attempts to resist work or authority. they have always been floating work camps run by a tyrant with full authority to maintain control.

the bullets for amall arms on large naval ships are intended for their own sailors should tensions come to a head.