HMS Sidon was launched in September 1944, one of the third group of S-class submarines built by Cammell Laird & Co Limited, Birkenhead.

On the morning of June 16, 1955, Sidon was moored alongside the depot ship HMS Maidstone in Portland Harbour. Two experimental torpedoes, code-named "Fancy," had been loaded aboard for testing. 56 officers and crewmen were aboard.

At 08:25, an explosion in one of the Fancy torpedoes (but not the warhead) burst the number-three torpedo tube it was loaded into and ruptured the forward-most two watertight bulkheads. As always in explosions aboard submarines, fire, toxic gases, and smoke accompanied the blast. Twelve men in the forward compartments died quickly and seven others were seriously injured.

The submarine started to settle by the bows with a list to starboard, and her commanding officer, Lieutenant Commander Verry, ordered the ship evacuated from the engine room and after escape hatches. Thanks to a rescue party from Maidstone, everyone not immediately killed escaped, except Maidstone's medical officer. He had gone aboard with the rescue party, assisted several survivors, and collapsed, unnoticed, in the control room after everyone else had left. At about 08:50 Sidon sank to the bottom of the harbour.

One week later the wreck was raised and towed into a causeway on Chesil Beach. The bodies of the 13 casualties were removed and buried with full honours in the Portland Naval Cemetery on top of the cliffs overlooking the harbour. A Court of Inquiry cleared anyone aboard Sidon for the loss of the boat. The direct cause of the accident was determined to have been malfunctioning of the "Fancy" torpedo, and that torpedo program was terminated.

A torpedo being readied for the morning test shot had begun a "hot-run" -- its engine had started while it was still inside the submarine and was over-speeding, creating very high pressures in its fuel system. The "Fancy" torpedo used "High Test Peroxide" (HTP) as an oxidizer. When an oxidizer line burst, HTP sprayed onto the copper fittings inside the torpedo, decomposing into oxygen and steam. The torpedo's warhead did not detonate, but its hull burst violently, rupturing the torpedo tube and causing the flooding that destroyed the boat.

It is likely that similar circumstances initiated the sequence of events that caused the loss of Kursk on August 12, 2000.

Sidon was refloated, and sunk as an ASDIC target on June 14, 1957.

See HMS Sidon for other ships of this name.

General Characteristics

• Displacement: 814-872 tons surfaced, 990 submerged
• Length: 217 feet (66 m)
• Beam: 23.5 feet (7.1 m)
• Draught: 11 feet (3.3 m)
• Speed: 14.75 knots (27 km/h) surfaced, 8 knots (15 km/h) submerged
• Armament: one three inch (76 mm) gun, one 20 mm antiaircraft gun; three .303 machine (~7.7 mm) guns
• Torpedo Tubes: seven 21 inch (533 mm) six forward, one aft, 13 torpedoes
• Complement: 48