reissued to new ships. The flag superior for whole ship classes has often been changed while the numbers stayed the same. For example, in 1940, the Royal Navy swapped the letters "I" and "D" around (e.g. D18 became I18 and I18 became D18) and in 1948, "K", "L" and "U" all became "F"; where there was a conflict, a 2 was added to the front of the pendant number. During the 1970s, the service stopped painting pennant numbers on submarines on the grounds that, with the arrival of nuclear boats, they spent too little time on the surface, although submarines do continue to be issued numbers. was initially allocated the pennant number F232, until it was realised that in the Royal Navy, form number 232 is the official report for ships that have run aground; sailors being superstitious, it was quickly changed to F229. Second World War No flag superior Pendant number 13 was not allocated. Capital ships, aircraft carriers, cruisers Flag superiors Pendant numbers 13 were not allocated to flag superiors. The letters J and K were used with three number combinations due to the number of vessels. D — destroyers (until 1940), capital ships, aircraft carriers, cruisers (from 1940) F — destroyers (until 1940) and large auxiliary combatants (from 1940) G — destroyers (from 1940) H — destroyers I — capital ships, aircraft carriers, cruisers (until 1940), destroyers (from 1940) J — minesweepers K — corvettes, frigates L — escort destroyers, sloops (until 1941) M — minelayers N — minesweepers P — sloops (until 1939), boom defence vessels (until 1940) R — destroyers (from 1942), sloops T — river gunboats, netlayers U — sloops (from 1941) W — tugs and salvage vessels X — special service vessels Z — gate, mooring and boom defence vessels 4 — auxiliary anti-aircraft vessels FY — fisheries (auxiliary fishing trawlers, drifter etc.) Flag inferiors Flag inferiors were applied to submarines. Royal Navy submarines of the "H" and "L", and some transferred American vessels, were not issued names, only numbers. In these cases, the pendant number was simply the hull number inverted (i.e. L24 was issued pendant "24L"). Pre-war photos show the pendants painted correctly, with the flag inferior, but wartime photos show that the numbers tend to be painted "backwards", in that the inferior was painted on as a superior. For obvious reasons, the inferior "U" was not used so as not