The Germans launched an attack preceded by poison gas at Ypres on 22 April. On 23 and 24 April the 1/4th Bn force-marched towards the Ypres Salient and went into the firing line on 26 April, digging new assembly trenches on a reverse slope. At 14.30 the battalion moved up in support of a British counter-attack, but the attack had failed, and the Londons marched across open ground under shrapnel shell fire to a sunken lane where the remnants of the attackers were sheltering. Here they dug a new temporary line. The following day the attack was renewed, the battalion coming under fire as it crossed the crest line. Heavy casualties were suffered in the valley beyond, until the battalion was withdrawn into brigade reserve after nightfall. The Ferozepore Brigade was relieved on 30 April and withdrew under shellfire. Between 26 and 30 April the 1/4th Londons had lost 365 out of 600 men; while withdrawing it was joined by a draft of 50 from the 3/4th Londons.