U-33

U-33 was detected while on mine laying duties in the Firth of Clyde during World War II. Attacked by depth charges, the submarine was eventuially scuttled in the waters to the south of Arran. Significantly, the crew failed to destroy previously unknown rotors for the Enigma machine, and these were captured.

There is a story circulating in the folklore of Dunoon that a U-Boat was depth charged and sunk outside the Cloch boom that ran between the town and the Cloch Lighthouse, and became the Skelmorlie U-Boat. While research has cast some doubt on this particular story, it has unearthed an equally interesting story regarding the sinking of U-33.

U-33 sinking

In early February 1940, U-33 was despatched to lay a minefield in the Firth of Clyde. As this was considered to be a dangerous mission in enemy waters, the Enigma coding machine which would normally be being carried on board was to be left behind, but this additional requirement was overlooked in the midst af all the other preparations for the mission.

In the early hours of June 12, 1940, U-33 was cruising slowly up the firth, on the surface. Through the darkness, the U-Boat's lookouts spotted a ship passing them in the opposite direction - this was the minesweeper HMS Gleaner, captained by Lt Commander Hugh Price. The lookouts thought they had gone undetected, but the ASDIC operator on Gleaner had picked up the sound of their diesel engines, and the minesweeper came about to investigate. The lookouts spotted Gleaner's approach at full speed, and the U-Boat crash dived, but the water was shallow and the vessel hit the seabed. Over a period of several hours U-33 survived two depth charge attacks, but had become stuck in the muddy seabed. The only way to break free was to blow all tanks and surface. Unknown to the crew of the trapped U-Boat, the last depth charge attack had damaged Gleaner's ASDIC, and they could have remained submerged and made their escape later. Unaware of Gleaner's problem U-33's captain, Lt Hans Wilhelm Von Dresky, decided to surrender, and charges were set to scuttle the boat after it had been abandoned.

Of the U-33 crew, 17 survived, but 25 died. They were taken to the German War Cemetery in Cannock Chase for burial.

U-33 sank in waters to the south of Arran.

Enigma code wheels

It was the job of three crew members to take the code wheels from the Enigma machine and jettison them from the submarine. One crew member became confused and failed to jettison wheels VI, VII and VIII. These were found on him and sent on to Bletchley Park, where they subsequently allowed all German naval messages to be decrypted.

The Kriegsmarine (German Navy) used a more complex Enigma procedure than the Army or Air Force, eventually providing eight rotors from which the three would be used at any time. The German Army and Air Force used only five. U-Boat traffic increased the complexity/security further by introducing a fourth rotor. The three wheels recovered included two of the extra wheels, VI and VII, providing valuable new information to the codebreakers as their wiring had previously been unknown.