In the centre , the main attack along the Buin Road began at 08 : 30 on 20 May after 20 minutes of strafing by New Zealand Corsairs had prepared the ground . Advancing under a creeping barrage , and with mortar and machine gun support , the 24th Infantry Battalion moved forward with three companies up front and one held back in reserve , along with two troops of Matilda tanks . Mostly the forward companies reached their objectives , but one of the companies was halted just short of their objective and was forced to dig @-@ in overnight after coming under heavy small arms and artillery fire and losing four killed and five wounded . The attack was resumed the following day , and the Australians were able to advance to the Pororei ford ; however , they were prevented from moving any further as the Japanese were still concentrated in large numbers further to the west where an Australian patrol encountered 70 Japanese and were forced to go to ground . Finally , a company from the 24th Infantry Battalion was able to move on to the high ground on Egan 's Ridge , which they found to be heavily mined and booby trapped . Engineers and assault pioneers were called up to clear the feature .