port. Acroma, Knightsbridge, south of Acroma and El Adem, were sited to block tracks and junctions. A box at Retma was finished just before the Axis offensive but work on boxes at Point 171 south-east of Bir Hakeim and Bir el Gubi did not begin until 25 May. Prelude British preparations Churchill pressed Auchinleck to attack to push the Axis out of Cyrenaica and relieve the pressure on Malta, which Churchill felt was essential to the war effort, The Eighth Army received new equipment, including tanks equipped with 75 mm guns, and large numbers of 6-pounder anti-tank guns. Rommel thought that Allied minefields ended well north of Bir Hakeim and did not know of the "mine marsh" surrounding the box. The Eighth Army was in the process of reorganising, changing the relationship between infantry and artillery, while the RAF commander Arthur Tedder concentrated the efforts of the Desert Air Force (DAF) on supporting the troops on the ground. Army commanders lost the power to direct air operations, which was reserved for the air commanders. A new fighter-bomber concept was developed and Air Vice-Marshal Arthur Coningham, commander of the DAF, moved his headquarters to the Eighth Army HQ to improve communication. Axis commanders knew that the entry of the United States into the war would give the Eighth Army access to an increase in materiel but sought to forestall an Allied offensive before these supplies could influence events. By late May, the 1st South African Division was on the Gazala line nearest the coast, the 50th (Northumbrian) Infantry Division to the south and the 1st Free French Brigade furthest south at Bir Hakeim. The 1st and 7th Armoured Divisions waited behind the main line as a mobile counter-attack force, the 2nd South African Division formed a garrison at Tobruk and the 5th Indian Infantry Division (which had arrived in April to relieve the 4th Indian Infantry Division) was held in reserve. The Allies had and Axis preparations The Axis retreat to El Agheila after Operation Crusader reduced the supply distance from Tripoli to . The discovery of of fuel at Tripoli eased the supply crisis, despite the delivery of only of supplies in January. The had a much shorter supply line and the British were burdened by an over-extended supply line. II in Sicily had also regained air superiority for the Axis. Rommel asked for another but this unrealistic demand was