HMS SIMOOM (Lt G Milner) was the first Cammell Laird built S-boat to be completed with a radar set installed. She completed a series of comparison trials with the captured U-boat HMS GRAPH (ex-U570).

She sank the Italian destroyer Vincenzo Gioberti in August 1943 and was on patrol in the Aegean when she was lost with all hands. She was probably mined between 4 and 6 November 1943.

A recent reconstruction of her patrol suggests that her route probably took her through a German anti-submarine minefield during daylight and therefore submerged and vulnerable.

NOTE: In 2016 the wreck of HMS SIMOOM was found about six nautical miles north-west of the Turkish Aegean island of Bozcaada (Tenedos) in 67 meters of water. Extensive damage was noted near the starboard hydroplane, and it was assessed that HMS SIMOOM hit a mine while running on the surface.