U.S. submarines are, like the rest of the armed forces, under tremendous pressure to cut costs. One novel way to do it is to reduce the number of expensive weapons in use. An American nuclear attack submarine carry 12 Tomahawk missiles and a combination of 28 Mk48 torpedoes/Harpoon missiles/Tomahawk missiles/Mines. That's over a hundred million dollars worth of complex weapons. Since not all attack submarines are at sea at the same time, money is saved by having only enough weapons for the ships at sea. When a ship comes back, it transfers it's weapons to the sub going out next. This is a lot of extra work for the crews, but it saves a few bucks and makes the brass look good.