This was a British midget submarine attack on the floating U-boat dock in the harbour of the Laksevåg area of Bergen toward the eastern end of the Puddefjord on the west coast of Norway (3/13 September 1944).
There were two such attacks, both by the midget submarine X-24, on this very heavily defended port in German-occupied Norway. In both raids the midget submarine was towed across the North Sea by the patrol submarine Sceptre, escorted by the patrol submarine Alecto, to minimise the exertions of its crew members before the attack by using a dedicated passage crew which was replaced by the operational crew once the boat was near the target area.
The first raid took place on 14 April 1944 as ‘Guidance’ (ii). Five months later, on 11 September, the boat again penetrated 30 miles (48 km) of fjord and negotiated the mine and net defences to enter Bergen harbour. Commanded by a British officer, Lieutenant H. ‘Percy’ Westmacott, with a different three-man crew, the boat’s target on this occasion was again the floating dock which had been towed from Germany to facilitate the completion of repairs on U-boats operating from Norwegian bases. It was believed that the dock could handle ships as large as the battleship Tirpitz, but it had been regularly used for the maintenance of U-boats.
The attack was delivered after a passage from England lasting 80 hours in extremely bad weather. On this occasion X-24’s attack was made in full daylight and the boat went through the crowded harbour at periscope depth, dodging ferries, tugs and other small craft before reaching the dock, diving under it, and releasing its two 2-ton side charges, all unseen, between 08.00 and 09.00. The explosion of the charges broke the dock into two pieces, which sank together with two small merchant vessels secured alongside, Sten and 914-ton Kong Oscar II.
By 20.30 in the evening of the same day X-24 had surfaced and was in contact with Sceptre and Alecto, and the boats reached Balta Sound, in the Shetland islands group, at 09.00 on 13 September.