In 1927 HMS M2 became the worlds first undersea aircraft carrier - a submarine carrying a small two-seater seaplane in a watertight hangar. The seaplane, which had folding wings, was launched by catapult off a runway on the deck. When it landed near the sub, it was hoisted on board and into the hangar by a specially designed small crane.The M2s crew was proud of the speed with which it could launch the little floating plane. Rising to periscope depth, the submariners would check around for enemy ships, surface, open the hangar door and catapult the plane off on its flight. They were constantly trying to beat their own speed record.It was this speed which was to kill all the crew. The M2 dived at 10.11am during exercises off Portland on 26 January, 1932, and disappeared. On 29 January all hope was officially abandoned for the 60 crew aboard.It took eight days to find her. The first divers discovered that the hangar door was open with the plane still inside. The hangar had apparently been opened while she was still underwater. A salvage operation retrieved the plane, but after 11 months and a total of 1500 dives involving 26 Royal Navy divers, the Admiralty had to admit defeat over the submarine. On 8 December, 1932, the M2 was left to rest forever on the seabed off Portland. (from scimitardiving.co.uk)