'Source' (i) was a British naval attack on the German battleship Tirpitz and, it was hoped, other targets such as the battle-cruiser Scharnhorst and heavy cruiser (ex-pocket battleship) Lützow, by midget submarines (20/22 September 1943).
The concept for the attack was developed by Commander J. Cromwell-Varley, with support of Admiral Sir Max Max Horton, commanding the British submarine arm, and Prime Minister Winston Churchill.
The operation was controlled from Varbel, the base located at Port Bannatyne on the Isle of Bute and named for Varley and commander Bell, designers of the 'X' class prototype, was the on-shore headquarters for the midget submarines of the 12th Submarine Flotilla. All midget submarine training and preparation for 'X' class submarine attacks was co-ordinated from Varbel.
Intelligence contributing to the attack on Tirpitz was collected and sent to the Royal Navy by members of the Norwegian resistance, especially brothers Torbjørn and Einar Johansen.
Under the command of Captain W. E. Banks, the 12th Submarine Flotilla had been established on 17 April 1943 to train midget submarine crews and develop the appropriate tactics for the attack planned by the staff of Rear Admiral C. B. Barry. The midget submarines were to be towed to within a short distance of the target area by parent boats, and between 30 August and 1 September these larger boats arrived at Loch Cairnbawm in north-western Scotland for final trials and training.
On 11/12 September the force departed with the submarines Truculent, Syrtis, Sea Nymph, Stubborn, Thrasher and Sceptre towing X-6, X-9, X-8, X-7, X-5 and X-10 respectively toward northern Norway.
The exact location of Tirpitz and the other possible targets was as yet uncertain, but it was anticipated that photo-reconnaissance would reveal this in time for final instructions to be radioed to the attack force, and the attack information was in fact sent on 14 September, this establishing that X-5, X-6 and X-7 would attack the Tirpitz in the Kåfjord subsidiary of the Altafjord, X-9 and X-10 would attack Scharnhorst in the Kåfjord, and X-8 would attack Lützow in the Langefjord, another subsidiary.
Six 'X' class craft were used. X-5, X-6 and X-7 were allocated the battleship Tirpitz in the Kåfjord. X-9 and X-10 were to attack the battle-cruiser Scharnhorst, also located in the Kåfjord. X-8 was to attack the heavy cruiser Lützow in the Langfjord. The midget submarines were towed to the area by conventional submarines: Truculent towed X-6 Syrtis towed X-9, Sea Nymph towed X-8, Thrasher towed X-5, Stubborn towed X-7 and Sceptre towed X-10), all the midget submarines being manned by passage crews on the way until, at points close to the intended targets being replaced by the attack crews. X-9, while commanded by Sub-Lieutenant E. Kearon of the passage crew and probably trimmed heavily by the bow in the heavy sea for the tow, was lost with all hands on 16 September during the passage when her tow parted and she suffered an abrupt plunge as a result of its bow-down trim. One day later, X-8, while commanded by Lieutenant J. Smart) developed serious leaks in her side-mounted demolition charges, which had to be jettisoned; these exploded, leaving the midget submarine so badly damaged that it had to be scuttled. The passage to the north was thus full of incident, including the parting of several tows.
The remaining X-craft began their runs to the targets on 20 September, and the attacks took place on 22 September from 19.00.
Scharnhorst was engaged in exercises at the time, and was thus not at her normal mooring. X-10's attack was abandoned, although this was the result of mechanical and navigational problems, and the midget submarine returned to rendezvous with its 'tug' submarine for return to Scotland.
Commanded by Lieutenant H. Henty-Creer, X-5 disappeared with her crew during 'Source', and is believed to have been sunk by a direct hit from one of Tirpitz's 105-mm (4.1-in) tertiary-battery guns before its demolition charges could be placed, although there is the possibility that X-5 did managed the successful planting of its side charges before being destroyed, but this was never conclusively proved. (An expedition in 2006 mapped the north and south anchorages used by Tirpitz and proved that the charge was well inside the net enclosure of the north anchorage and therefore most likely from X-6.)
X-6 and X-7 successfully dropped their charges under Tirpitz, but were unable to escape as they were observed and attacked. The crew of X-6 scuttled their craft and were picked up by the Germans, who then warped Tirpitz away from the position where X-6 had gone down and thus away from this boat’s charges. X-7 placed both her charges and then tried to escape, only to find the gate in the anti-torpedo booms closed. The boat was then damaged and its commander decided to abandon the boat after the crew had scrambled onto a nearby gunnery target. The commander got onto the target but the boat then sank, only one of the three men still on board managing to escape with the aid of his escape gear.
Upon capture, the crewmen informed the Tirpitz's captain, Kapitän Hans Meyer, that there would be explosions below his ship within an hour. Meyer quickly attempted to warp his ship away from the charges, but was unable to do so before the charges exploded.
Tirpitz was severely damaged. While not in danger of sinking, she took on more than 1,400 tons of water and suffered significant mechanical damage. The first charge exploded abreast of the 'Cäsar' turret and the second 150 to 180 ft (45 to 55 m) off the port bow. A fuel oil tank was ruptured, armour plating was torn, a large indentation was made in the bottom of the ship, and bulkheads in the double bottom were buckled. Sea water flooded into the some of the ship’s fuel tanks and void spaces in the double bottom of the port side, which caused a list of 1° to 2° that was then balanced by counter-flooding on the starboard side. The flooding damaged all of the turbo-generators in the no. 2 generator room, and all apart from one generator in the no. 1 generator room were disabled by broken steam lines or severed power cables. The 'Dora' turret was thrown from its bearings and therefore could not be traversed; this was particularly significant, as there were no heavy-lift cranes in Norway powerful enough to lift the turret and place it back on its bearings. The ship’s two Arado Ar 196 floatplanes were tossed by the explosive concussion and completely destroyed. Repairs were conducted by the repair ship Neumark and lasted to 2 April 1944. Full-speed trials were scheduled for the following day in the Altafjord.
The explosion which caused the damage to X-7 was the simultaneous detonation of all four charges at 08.12. Although Tirpitz was not irretrievably crippled, she was very badly damaged as the concussion lifted the ship several feet into the air to come down with so great a shock that all three sets of main propulsion turbines were badly damaged.