Navigation: 1 mile offshore from the Grand Harbour
Access: Boat Dive
Depth: 73 metres
Sea Bed: Silt
Interests: Deep and Wreck Diver
Certification Required: Tec divers only
The outside of S-Boats were covered by mahogany casing, with an internal hull of light metal, which have rotted away. S-31 had three Daimler Benz MB502 diesel engines = 4800 BHP total, with 3 propellers. Maximum speed 38 knots. Range - 800 sea miles at 30 knots. Armament: 2 x 533 mm torpedo tubes, 2 x 20mm guns. Crew: 24 men. At the time of loss S-31 had 2 Italian officers as observers, who were among the survivors.
It belonged to a sub-group numbered S-30 to S-37, built by Lurssen at Vegesack, which were launched and commission in 1939. During the afternoon on the 9th May 1942 intelligence through the Luftwaffe indicated that the Welshman, which was making a solo run to Malta, would arrive at Valletta before dawn on 10th May 1942. So the German 3rd MTB Flotilla carried out an operation to intercept the mine layer as she approached Valletta harbour from the north east, which was the normal direction of approach to Valletta by the British warships at that time.
Four MTBs (S-54, S-56, S-57 & S58) would wait for Welshman off the St Thomas area to attack her as she approached up the SE coast. Three other MTBs (S-31, S-34, and S-61) were first to lay a minefield stretching out off Sliema point in order to cover this side should Welshman approach Valletta via the northwest instead - this would be a fresh minefield which the British would have had no time to clear. After laying this minefield the three MTBs were to go eastwards to add their torpedoes against Welshman.
The 7 MTBs left Augusta at 2200 of the 9th May 1942 and at 0414 of the 10 May the three MTBs began laying the minefield which was in the shape of an isosceles triangle. The minefield consisted of 20 FMC mines (contact mines), 6 explosive buoys and 2 cutting buoys and it was completed at 0421 (7 minutes). The three MTB had to regroup, & go eastwards in search for Welshman, but suddenly one minute after the lay had stopped S-31 exploded a mine, probably one S- 31 had just laid and had cut loose from its moorings, rising to the surface and drifted into S-31. She sunk at 0438, S-61 managed to save 13 survivors including C.O. Lt. Heinrich Haag, 13 others died.