Royal Army Service Corps (RASC) 152/51 and 235/89 HAA Btys each had two captured Italian 102mm guns in addition to their 3.7-inch guns; the LAA Bty was manning a mixture of Bofors 40 mm guns, Italian Breda 20mm guns and LMGs. General Erwin Rommel had attacked with his Afrika Korps in Cyrenaica in April 1941, forcing the British Western Desert Force (WDF) back past Tobruk. 51st (London) HAA Rgt had retreated inside the Tobruk perimeter, and had been reinforced by sea by 235 (Kent) HAA Bty with static 3.7-inch guns just before the ring closed round the port on 11 April, beginning the epic 240-day long Siege of Tobruk. The Official History records that the AA artillery was 'incessantly in action against attacks of all kinds, from all heights, but especially by dive-bombers'. The usual targets were the harbour, airfields, base installations, and the AA and field gun positions. Early in the siege, RHQ and 152 HAA Bty of 51st HAA Rgt were attacked by Junkers Ju 87 Stukas and suffered serious casualties; the RHQ was evacuated by sea and had to be replaced temporarily by HQ of 13th LAA Rgt. After RHQ of 69th HAA Rgt arrived to take over, it was followed by 192 HAA Bty to relieve 152 HAA Bty. The Royal Artillery historian notes that the Stuka attacks concentrated on gun positions, which was a serious threat to HAA sites, whose instruments could not cope with the rapid height changes. The gunners devised a tactic of opening fire with short fuzes just before the dive started, to force the pilots to fly through a ring of bursts. The battery cooks, drivers and clerks then joined in, firing LMGs and captured Bredas. This aggressive method was known as 'Porcupine', and was so effective that the Luftwaffe changed to high-level bombing. For example, on 27 August and 1 September, RHQ's Bren and Lewis LMGs were in action against raids by Junkers Ju 88s and Ju 87s; on the latter day they claimed hits against two Ju 87s, 'which went off smoking and appeared to be in trouble'. Each mobile HAA troop established at least one alternative site and the guns were regularly switched between them, the empty sites being rigged up as dummies. The two available GL radar sets had to be positioned away from the vulnerable gun sites and used for early warning to supplement the single