Since early in the war the Royal Navy considered methods that could be employed to disable the German Battle cruiser Tirpitz. This ship presented a major threat to Atlantic convoys, particularly the Arctic convoys to Murmansk in northern Russia. Usually carefully concealed at the head of a long Norwegian fjord, the position of the German battleship at the time rendered it impossible to attack from the air. One alternative method led to the design, trials and development of a 44 ft. midget Submarine called the X craft. It had a beam of 5ft 6 ins. This craft was designed to carry a crew of 4, including a diver to cut through anti submarine nets. Under command of a Royal Navy Officer, the X craft was a complete submarine in miniature. Propelled on the surface by a 44 hp. Gardner diesel engine, it could submerged to 300 ft driven by an electric motor. (the engines were built at the Gardner Engine Company's Patricroft works in Manchester.) The X craft was intended to be towed by a parent submarine to near the scene of operations. There a passage crew would be exchanged for the operational crew, who would press home the attack. The midget submarine was equipped with two 30ft long side charges containing 2 ton of amatex explosive. These were carried on the outside of the craft, and would be released to be left on the seabed under the target ship. The charges would be detonated by a delayed timing device.
The X Craft Unit was formed within the 12th submarine flotilla RN in the south of England through the winter of 1941/2. The first prototype X craft X 3 was built in Portsmouth and was launched near Southampton in March 1942. X 4 was a foot longer at 45 ft. Recruitment and training of operational personnel commenced in April. A top secret shore base 'HMS Varbel' was established ( under the Command of Commander T.I.S. Bell RN who with Commander Varley had designed and supervised the building of X3 and X4 ) at Rothesay on the Firth of Clyde. By the late summer of 1942 the crews were housed, at the 12th Flotilla Diving training center. This was a requisitioned shooting lodge (HMS Varbel II) on Loch Striven. ( It was only at this stage that SOE formed ISRB.) Following successful trials with prototypes X3 and X4 12 larger craft were commissioned from Vickers Armstrong. (these were 51ft long with a beam of 5ft 9 ins, the extra length allowing a 4ft long Wet & Dry compartment to be created, for use by a diver) (Some reports suggest that X craft segments were actually constructed at several different locations around the UK such was the secrecy surrounding the project). The craft were delivered by rail to the Royal Navy at Faslane on the Clyde for final assembly. The allocation of the depot ship HMS Bonaventure, a heavy lift cargo ship, to the 12th Flotilla allowed advanced training to take place, at many West Coast locations, through the summer of 1943. The remote sealoch Loch Cairnbawn Port HHZ in North west Scotland became the main sea training base.
On 11th September 1943 six X craft (X 5 - X 10) were dispatched from Port HHZ towards Norway. Three were deployed to attack the 40,000 ton battle cruiser 'Tirpitz', now concealed at anchor deep within the Kaafjord in northern Norway. The others were to attack the 'Lützow', and the 'Scharnhorst', also in Norwegian waters. Each X craft set out from p under tow by a parent submarine for the 1000 mile, 8 day and night crossing to Norwegian waters. 5 days out from home X9 disappeared along with its passage crew when the tow line parted. In spite of a long search neither the craft nor its passage crew of three were ever found. The tow of X 8 also parted , but after a 36 hour search she was recovered, and the tow resumed. However one side cargo developed leaks, upsetting the trim. Set to explode at some distance from the craft it detonated early causing further damage. Later the second leaking side cargo was also released. In spite of setting an even longer delay on the the fuse it also exploded prematurely resulting in yet more damage to the X craft, but also to the towing submarine. The X craft became impossible to handle. The passage crew was transferred off X 8 and she was scuttled. X10 also experienced severe technical problems while under tow, and was delayed
missing her opportunity to attack.
Only X 7 and X 6 are known to have pressed home their attack to drop their amatol charges, on delay fuses, below the battle cruiser. X 6 sustained damage and was forced to the surface. The commander ordered the destruction of all secret papers and equipment, then ensured that his crew got out before scuttling X 6 under the Tirpitz itself All four X6 crew were quickly captured and taken aboard Tirpitz. Soon afterwards X 7, which had become ensnared in the anti submarine nets surrounding Tirpitz, was caught by the huge explosion of the four 2 ton charges, and sank to the seabed. During the next four hours two of the crew of X7 escaped from the submerged craft (a technique practiced during their DSEA training) and were also captured. However two of the crew of X 7 did not manage to escape and drowned within their craft. X 5 mysteriously disappeared with her complete crew, while close to the target. Whether X 5 also breached the torpedo nets surrounding 'Tirpitz' and was lost while attempting to escape afterwards is an open question. The damage to 'Tirpitz' was so extensive that she was never returned to service. The award of the Victoria Cross was made to Lt. D. Cameron commander of X 6 and to Lt. G. Place commander of X 7, for their outstanding heroism during the operation.
After evading through hostile seas for over a week X10 eventually managed to rendezvous with a recovery submarine
but was subsequently scuttled during the long trip home.
At its conclusion the Operation 'Source', to cripple a battleship, had cost the lives of 9 men and the loss of all six X craft.
( It is relevant to note the further action was undertaken a year later against the Tirpitz, which by then had almost been repaired. The RAF attacked her using 12,000 lb bombs on 15th Sept 1944. A final RAF raid on 12th November 1944 involving 32 Lancaster bombers with 12,000 lb bombs scored 3 direct hits. From almost 1300 crew on board, there were only 76 survivors.)
[ Note: By early October 1943 six more craft were under construction. The contracts were placed with three civilian engineering companies: two craft with each. X20, and X21 were built by Thomas Broadbent & Co in Huddersfield. X22 and X23 were built by H.V. Markham & Son in Chesterfield. X24 and X25 were built by Marshall in Gainsborough. These new craft incorporated the many improvements developed for the earlier series. During early 1944 another 4 lightly equipped 51 ft. training craft XT 1 - 4 were built. By early 1945 following the construction of a further two 53ft. XT craft and 6 53ft. XE's (for use in the Far East) more than 22 X craft were in existance].