Although the box was isolated by Axis troops, it held out, with the HAA guns in two-gun detachments engaging tanks, vehicles and guns at close range with High explosive, Armour-piercing and Shrapnel shells. The brigade also lent troops of Bofors guns to roving 'Jock columns'. Eventually, Eighth Army was forced to evacuate the boxes and retreat towards Egypt, the garrison of El Adem slipping away during the night of 17 June. Tobruk was captured on 21 June, including 4 AA Bde HQ and a number of 12 AA Bde's detached units (RHQ, 277 and 282 Btys of 88th HAA Rgt, 107 Bty of 27th LAA Rgt). Conversely, 14th (West Lothian, Royal Scots) LAA Rgt of 4 AA Bde was outside the perimeter and. escaped capture: it was 'picked up' by 12 AA Bde during the retreat. During the long retreat to the El Alamein position, 12 AA Bde, now under Brig Percy Calvert-Jones fell back in a series of rearguard actions at LGs, in the course of which it concentrated a sizeable body of troops: 88th and 94th HAA Rgts, 2nd, 14th, 15th (Isle of Man), 16th, 27th and  42nd LAA Rgts, two S/L troops and some motorised infantry. Eighth Army seized upon this collection to act as a blocking force, giving Calvert-Jones two infantry brigades in addition. 'Calforce' held defensive positions at 10 LGs, providing its own artillery support from AA guns sited for ground tasks. It also developed dummy LGs, complete with fake AA positions. Calforce remained in position during the First Battle of El Alamein, had 9th Independent Armoured Bde under its command from 26 August to 8 September, and was not withdrawn from the front line until later in September. After 12 AA Bde was withdrawn from its front line commitments, it reorganised for the planned offensive (the Second Battle of El Alamein) as follows:   12 AA Bde was directly subordinate to Eighth Army, which placed 21 Indian Infantry Bde under its command:  12 AA Brigade's role once again was to move up behind Eighth Army's advance and defend the DAF's LGs as they came into use, with batteries working under the command of the DAF tactical wing to which they were allocated.