The siege of Tobruk ended on 10 December 1941

Tobruk had been besieged by Axis forces since 11 April 1941. On 10 December, the siegde was lifted when the Italian Trento and Brescia Divisions withdrew from the west side. The original expectation was that the siege would be lifted early in the Crusader Battle. In fact, there were three weeks of combat before the Axis forces were depleted enough to be forced to withdraw. Transport had been the greatest challenge, because supplies had to be carried from the railhead, by road, to the forward forces. Simply lifting the seige was not enough to fix the supply problem, as much work would be required before the port of Tobruk would be up and receiving supplies by sea in sufficient quantity to meet the army's needs. A supply center had yet to be built up and that would take time. Still, the enemy's withdrawal from around Tobruk allowed the air forces to redeploy to fields much further forward, which extend British air superiority over the new battlefield. This is based on the account in Vol.III of the Official History.