April, while more work was done on the defences. Once inside, the three 9th Australian Division brigades took over the defences and the 18th Brigade went into reserve. A cadre of the British 3rd Armoured Brigade was refitting at Tobruk, with personnel and equipment sent from Egypt by sea and had a regiment of armoured cars, two composite regiments with 15 light, 26 cruiser and a troop of four infantry tanks. There were four 25-pounder regiments, two anti-tank regiments and an anti-tank company in each infantry brigade, the British 4th Anti-Aircraft Brigade had sixteen heavy and fifty-nine light guns, all but two Bofors guns being sited around the harbour. Rear area units had accumulated at Tobruk and of the were in base units or local refugees and prisoners of war. Morshead planned an active defence and stressed that, with battalions holding frontages, a break-in should be expected anywhere that the attackers made a serious effort and that it should be eliminated, since there would be no withdrawal. Siege Investment of Tobruk By 8 April, the most advanced German units had arrived at Derna; but some units which had cut across the chord of the Jebel Akhdar ran out of water and fuel at Tengeder. Heinrich von Prittwitz und Gaffron, the commander of the 15th Panzer Division, was sent ahead with a column of reconnaissance, anti-tank, machine-gun, and artillery units to block the eastern exit from Tobruk as the 5th Light Division moved from the southwest and the 27th Infantry Division "Brescia" advanced from the west. On 10 April, Rommel made the Suez Canal the objective of the and ordered that a breakout from Tobruk be prevented. The next day, the port was invested; but the rush ended with the 5th Light Division on the east side, the Prittwitz group to the south (Prittwitz having been killed), and the 27th Infantry Division "Brescia" to the west. Reconnaissance Unit 3 went on to Bardia, and a composite force was sent on to Sollum to try to reach Mersa Matruh. The British Mobile Force (Brigadier William Gott), on the frontier from Halfaya Pass to Sidi Barrani, conducted a delaying-action around Sollum and Capuzzo. El Adem road From the 5th Panzer Regiment probed the defences of the 20th Australian Brigade near the El Adem road. The tanks were held off by artillery-fire; German infantry who reached the anti-tank ditch were forced back by Australian