On 22 March 1917, 70th Siege Bty moved north to join 31st HAG with First Army, which was preparing for the Battle of Vimy Ridge. 31st HAG was assigned to I Corps with its batteries firing from around Bully Grenay on the extreme north flank of the attack, from where they could virtually enfilade the German lines. The artillery plan for the heavy guns emphasised counter-battery (CB) fire. At Zero hour, while the field guns laid down a Creeping barrage to protect the advancing infantry, the heavy howitzers fired further ahead to hit the rear areas on the reverse slope of the ridge, especially known gun positions. The attack went in on 9 April with I Corps and Canadian Corps successfully capturing Vimy Ridge while Third Army attacked further south near Arras. The only hold-up on 9 April was at Hill 145, near the north end of the Canadian attack, and the capture of this position was completed the next day. Fighting in the southern sector (the Battle of Arras) continued into May.