Tobruk was the only deep water port in Eastern Libya and as a consequence it had been heavily fortified by its former Italian garrison. The capture of Tobruk was essential for an advance on Alexandria and Suez.
In April 1941, German Field Marshal Erwin Rommel made its capture the main objective of his first offensive in North Africa. British forces in Libya's eastern coastal region of Cyrenaica were caught completely by surprise and retreated several hundred miles across the desert towards Tobruk.
Realising that he had a chance to capture Tobruk before the Allies had time to organise a defence, Rommel pushed forward. The 9th Australian Division, supported by British tanks and artillery, repulsed initial German assaults on 10-14 April 1941, and even when the fresh 15th Panzer Division was committed to the attack on 30 April, the defenders held on.
Under siege, the defenders had to adjust to life in stifling heat, under constant artillery and air bombardment. Supplies of food and water decreased, and the troops were plagued by flies, fleas and illness. Nevertheless, morale remained high - the Australians adopting the ironic nickname 'The Rats of Tobruk', in response to reports that Nazi radio propagandist 'Lord Haw Haw' had described them as being caught 'like rats in a trap' in one of his broadcasts.
The Australians provided the mainstay of the Tobruk defence force until August, when they were withdrawn and replaced by the British 70th Division, with the attached Polish Carpathian Brigade.
British forces lifted the siege on 10 December 1941 during Operation 'Crusader', when 1st Army Tank Brigade linked up with a 'break out' force from Tobruk - the 32nd Army Tank Brigade - at Ed Duda, to the south-east of the town.