This was a British carrierborne air attack by elements of Admiral Sir Henry Moore’s Home Fleet on the U-boat base at Kilbotn, 5 miles (8 km) to the south of Harstad in German-occupied Norway, and also to destroy shipping anchored at Sandnessjøen (1/10 May 1945).
'Judgement' (ii) was the last major undertaking by the Royal Navy in the European campaign of World War II, and was launched by 44 aircraft of the Fleet Air Arm operating from the escort carriers Queen, Searcher and Trumpeter steaming offshore escorted by the heavy cruiser Norfolk and light anti-aircraft cruiser Diadem of the 1st Cruiser Squadron, and destroyers Carysfort, Obedient, Opportune, Orwell, Savage, Scourge and Zambezi, supported by the oiler Blue Ranger, and all under the command of Vice Admiral R. R. McGrigor, second-in-command of the Home Fleet.
Between 1939 and 1945 the Germans made extensive use of the U-boat as a strategic weapon, and from bases in northern Norway U-boats were despatched to lay mines in Soviet waters and to attack the Allied convoys making for Soviet ports in the Arctic Ocean. In the autumn of 1944, when German forces retreated from the extreme north of Norway, the U-boat base at Hammerfest was relocated to Kilbotn farther to the south.
The base comprised the 5,000-ton depot ship Black Watch, a former North-Sea passenger ferry, supported by a Norwegian costal battleship converted by the Germans into a Flak ship, two barges fitted with anti-aircraft guns, and numerous gun emplacements on the land round the harbour. Several other ships were employed in ferrying supplies and ammunition to the base at Kilbotn, including the 950-ton Norwegian cargo ship Senja. The attack destroyed Black Watch and Senja and also U-711, which had been moored alongside Black Watch. Two British aircraft with the four men of their crews were lost, and an estimated 150 German personnel also lost their lives.
The attack force departed Scapa Flow in the Orkney islands Group on 1 May, and Trumpeter carried eight Grumman Avenger torpedo bombers and four Grumman Wildcat fighters of No. 846 Squadron, Queen carried eight Avenger and four Wildcat warplanes of No. 853 Squadron, and Searcher carried 20 Wildcat fighters of No. 882 Squadron.
The British were well aware of the strength of the defences at Kilbotn, and also of the fact that the Germans had a fighter base only 50 miles (80 m) distant to the east at Bardufoss. Four Wildcat fighters were assigned to provide top cover against any attempted intervention by German aircraft, while the most of the other Wildcat fighters were to arrive at Kilbotn at the start of the operation to attack the anti-aircraft gun emplacements on land and in the harbour. Eight of these latter Wildcat fighters were also armed with one 250-lb (113-kg) bomb with which to attack the Flak ship Thetis (formerly the Norwegian Harald Haarfagre), which was armed with seven 4-in (102-mm), two 40-mm and nine 20-mm guns. The Avenger attack aircraft were then to arrive, each armed with four 500-lb (227-kg) bombs, and carry out their glide-bombing runs in quick succession, No. 846 Squadron’s aircraft attacking Black Watch and No. 853 Squadron’s machines tackling Senja. The bombs were released at an altitude of 2,000 ft (610 m) after a glide from 6,000 to 8,000 ft (1830 to 2440 m).
The German early-warning systems in the Norwegian islands (radar, spotters and gun emplacements) could not have failed to observe and identify the aircraft passing over them, but fortunately for the British attackers the headquarters staff at Harstad failed to circulate a warning. As a result the airborne force, under the command of Lieutenant Commander C. L. F. Webb, arriving from the west over Kilbotn at 17.00 on a sunny afternoon, achieved almost complete surprise.
In the initial attack a Wildcat of No. 882 Squadron was hit and crashed into the water with the loss of the pilot. As the attack developed over the following seven minutes, several aircraft received Flak damage but the attack went according to plan. One Avenger of No. 846 Squadron made a forced landing which the three-man crew did not survive.
In the village of Kilbotn, 1 mile (1.6 km) from the mooring of the primary target, Black Watch, one bomb fell near some houses after a fault in the launching mechanism of one of the Avengers. With its time-delayed fuse it exploded after entering soft ground, which absorbed most of the splinters. Two houses suffered windows blown out and some damaged woodwork. The remaining 42 aircraft returned to the carriers.
On board U-711, the harbour crew of eight including the captain, Hans-Günther Lange, survived by moving the boat away from the vessels under attack, but the damaged boat sank some hours later, though the eight sailors were recovered.
The ships of the 1st Cruiser Squadron sailed south to provide air-cover for the passage of ships in the Skagerrak for 'Cleaver' and arrived back at Scapa Flow on May 10.
Some Allied ships were sunk by U-boats based in Norway until 7 May, even though it was later discovered that Germany’s final leader, Grossadmiral Karl Dönitz, had ordered the immediate cessation of all U-boat attacks on Allied shipping on 4 May, a few hours before the Kilbotn attack took place.