However, Caen did not fall on D-Day as planned, although a battalion of the British 3rd Division made a spirited attempt before being driven back by the 21st Panzer Division. Instead, Crocker's corps took part in the bloody two-month Battle for Caen, including Operation Charnwood, which still had the 3rd Canadian and 3rd British Divisions under command (the latter now under Major-General Lashmer Whistler after Rennie was injured), along with Major-General Lewis Lyne's 59th Division. The operation began on 7 July and, after heavy fighting, had captured most of the Caen city centre, although the Germans still held the southern half. The corps, losing the 3rd Division soon after and gaining Major-General Evelyn Barker's 49th Division in exchange, came under command of Lieutenant-General Harry Crerar's First Canadian Army in August 1944, I Corps drove forward to the River Seine and then took part in the unglamorous mopping up operations along the French and Belgian coastline. The relationship between Crocker and Crerar was not always cordial, with the latter, shortly after taking Crocker's I Corps under command of the First Army, attempted to sack Crocker and replace him with either Lieutenant-Generals Neil Ritchie (GOC XII Corps) or Gerard Bucknall (GOC XXX Corps). However, Crerar was overruled by General Montgomery, the 21st Army Group commander, although the relationship improved thereafter.