'Barbara I' was a British naval operation to sink shipping in the coastal waters of German-occupied Norway using 'Welman' one-man submersible craft each weighing some 2,000 lb (907 kg) excluding the 425-lb (193-kg) Torpex warhead, which was designed to be attached by magnets to the target’s hull (20 November 1943/5 February 1944).

The 'Welman' was developed by the Special Operations Executive. It only saw action only once, and was not particularly successful. Designed by the commander of the SOE’s Inter Services Research Bureau, Lieutenant Colonel John Dolphin, as a method of delivering a large explosive charge below an enemy ship, the 'Welman' was a submersible rather than true submarine vessel 20 ft 6 in (6.25 m) in length including its explosive charge, and weighed about 2,000 lb (917 kg) without this charge. Unlike the 'Chariot' human torpedo, the operator was enclosed within the craft, and did not need to wear diving gear. The 'Welman' could carry a 425-lb (1930kg) time-fused explosive charge of Torpex, which was intended for magnet attachment to a target’s hull. Vision was through armoured glass segments in the small conning tower, and no periscope was fitted. Propulsion was by a 2.5-hp electric motor, speed was 3 kt (5.6 km/h) and range 41.5 miles (67 km) at 3 kt.

Following trials in the Queen Mary Reservoir near Staines in Surrey toward the end of 1942, the 'Welman' was put into production by Morris Motors' requisitioned factory at Oxford.

Despite the craft’s inability to cut a way through anti-submarine nets, which both 'X' class submarines and Chariot manned torpedoes could do, and the poor fields of vision available to the 'pilot', 150 production examples were ordered in February 1943. Production was halted in October 1943 after operational research had revealed that the concept suffered from too many disadvantages, by which time some 100 examples had been manufactured.

In the autumn of 1943 Major General R. E. 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 30^th 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 departed Lunna Voe in the Shetland islands group 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.