How navies borrow weapons from other services

How often do navies borrow equipment from other branches or other navies?

Regularly, and wartime borrowing can be highly informal when useful weapons are sitting idle while ships face an immediate threat.

Navies regularly borrow equipment from other services and fleets. In one wartime anecdote, a British Army unit returned to a store of captured Italian antiaircraft guns and found that every gun had disappeared. After several weeks of searching, extra weapons resembling them were noticed aboard Royal Navy destroyers and sloops in the Mediterranean. The example concerns an informal transfer of weapons from storage to ships that could use them immediately.