battle for air superiority was mirrored by the air war over the sea as the Luftwaffe and Regia Aeronautica attempted to cut off sea traffic supplying the defenders. The air-sea battle, after the failure of Operation Battleaxe, was the main sector of operations for Allied and Axis aviation throughout the summer. Sturzkampfgeschwader 3, another Ju 87 wing arrived in Africa in the summer. The eight-month long siege was costly for the Stuka gruppen. At the end of April, virtually all Tobruk-based fighters had been removed from the encircled port. The Ju 87s were facing defenders with anti-aircraft artillery numbering 88 guns—28 heavy (90 mm or above). Ships lent their weapons to the defenders. In an example, the gunboat Ladybird, sunk in shallow waters to her deck by II./StG 2, was able to use her 3-inch deck guns. In April, Draco, Bankura, Urania, and were sunk by Axis aircraft. On 4 May the hospital ship Kapara (846t) was damaged evoking fury on the Allied side. The arrival of Italian Ju 87s from 97 Gruppo resulted in the sinking of the 3,741-ton tanker Helka on 25 May before it could reach Tobruk. The squadron involved, the 239 Squadriglia was the successful unit, which became among the most successful over Tobruk. The escorting sloop, Grimsby was damaged, and sunk by 3./StG 1. Commensurate with the sinking of Fiona and Chakla in April, the burden fell to the Mediterranean Fleet's destroyers to carry the burden but supply operations in daylight and on moonlit nights proved hazardous. On 24 June the sloop Auckland was sunk by 239 Squadriglia. This unit also sank the destroyer Waterhen. The vessel had just survived an attack by Junkers Ju 88s of III/LG 1 and II/StG 2. The lack of fighters made for a straight battle between the gunners and German pilots. The gunners changed their tactics from a sustained barrage at a fixed altitude, to a staggered, and thickened belt, at various altitudes covering 1000 metres or more, thereby forcing the Ju 87s to fly through fire for much longer. The gunners spread their fire from side to side, to prevent German pilots from travelling down the side of the barrage and sliding in underneath it. The Stukas were active in night operations. On 26/27 October 1941, I/StG 1 attacked a convoy transporting 7,000 British and Polish soldiers with munitions sailed toward Tobruk. An attack by the Ju 87s