'Enclose I' was a British air operation by Air Vice Marshal G. R. Bromet’s No. 19 Group of Air Marshal Sir John Slessor’s RAF Coastal Command in succession to 'Gondola' as the primary means of detecting, trapping and destroying U-boats transiting the Bay of Biscay (21/28 March 1943).
The offensive was based on the use of aircraft fitted with surface-search radar and searchlights to find and then illuminate for accompanying attack aircraft any U-boats running on the surface at high speed to escape the danger area. There were 28 sightings, resulting in 15 attacks, in the course of which one U-boat was sunk.
'Enclose I' involved 182 sorties, which achieved few sightings by day because the U-boats were running submerged, surfacing only to charge their batteries at night. However, on 21 March a Vickers Wellington of No. 172 Squadron, equipped with Leigh Light, damaged Oberleutnant Gerhard Wysk’s returning U-322. On 22 March a Wellington of the same squadron equipped with ASV.Mk IV radar as well as a Leigh Light sank Oberleutnant Hans-Jürgen Haupt’s U-665.
However, Kapitänleutnant Manfred Kinzel’s U-338 shot down a Handley Page Halifax of No. 58 Squadron on 22 March. 09.58 in the outer part of the Bay of Biscay, the inbound U-boat was surprised by the Halifax, but the boat’s accurate anti-aircraft fire during the attack run meant the stick of bombs fell wide, and only one detonating near the bow caused some light damage. The Halifax was hit in the outer starboard engine and fuselage and was seen to crash into the sea some distance away. The U-boat rescued the sole survivor of the aeroplane’s eight-man crew.