This could carry a small Parnall Peto seaplane, specially designed for the M2, which, once its wings had been unfolded, could be lowered onto the sea alongside by a derrick for take off.

[1] The submarine was intended to operate ahead of the battle fleet in a reconnaissance role, flying off her unarmed seaplane as a scout.

M2 left her base at Portland on 26 January 1932, for an exercise in West Bay, Dorset, carrying Parnall Peto serial N255.

Her last communication was a radio message at 10:11 to her submarine depot ship, Titania, to announce that she would dive at 10:30.

The captain of a passing merchant ship, the Newcastle coaster Tynesider, mentioned that he had seen a large submarine dive stern first at around 11:15.

In an operation lasting nearly a year and 1,500 dives, on 8 December 1932, she was lifted to within 20 ft (6 m) of the surface before a gale sprang up, sending her down to her final resting place.

The accident was believed to be due to water entering the submarine through the hangar door, which had been opened to launch the aircraft shortly after surfacing.

Two explanations have been advanced; The first is that since the crew were always trying to beat their record time for launching the aircraft, they had opened the hangar door on surfacing while the deck was still awash.

On 25 February 1932, a help message from M2, written in pencil on a small piece of wood, was discovered by a fisherman on the shore at Hallsands, south Devon.

It was handed over to the naval authorities and is now on display at the Royal Navy Submarine Museum in Gosport.