This was a British naval operation to sink shipping in the coastal waters of German-occupied Norway using 'Welman' one-man electrically powered submersible craft each weighing some 2,000 lb (907 kg) excluding the 425-lb (193-kg) Torpex warhead, which was attached by magnets to the target’s hull (20 November 1943/5 February 1944).
In the autumn of 1943 Major General Sir Robert Laycock, heading the Combined Operations Headquarters, decided that the 'Welman' was unsuitable for combined operations purposes, so the craft (about 100 of a total of 150 which had been ordered) were returned to the Royal Navy. Admiral Sir Lionel Wells, the senior naval officer in the Orkney and Shetland island groups, believed that the craft might prove useful for attacks on German shipping using coastal waters inside the Leads off Norway. The Norwegian-manned 30th Motor Torpedo Boat Flotilla was already making such raids, and agreed to try the 'Welman' craft in an attack on the floating dock in Bergen harbour, which was eventually sunk in September 1944 by the two-man midget submarine X-24.
On 20 November 1943 MTB-625 and MTB-635 left Lunna Voe in the Shetland islands carrying the 'Welman' craft W-45 (Lieutenant C. Johnsen of the Free Norwegian navy), W-46 (Lieutenant B. Pedersen of the Free Norwegian army), W-47 (Lieutenant B. Marris, RNVR) and W-48 (Lieutenant J. Holmes, RN).
The craft were launched at the entrance to the fjord. W-46 encountered an anti-submarine net and was forced to the surface, where it was spotted by a German patrol craft. Pedersen was captured, together with his 'Welman'. The other three craft, having lost the element of surprise, could not press the attack and so eventually had to be scuttled. Their operators made their way north with the help of Norwegian resistance members and were picked up in February 1944 by MTB-653.