While with the 3rd Division at Ypres, Mercer became the highest-ranking Canadian officer killed in action during the First World War.

On the same day, Brigadier V. A. Williams, commanding the 8th Infantry Brigade, became the highest-ranking Canadian officer captured in the First World War, also at the Battle of Mount Sorrel.

The division's 8th and 9th Canadian Infantry Brigades began embarking as early as 1 July 1941 and arrived in the United Kingdom at the end of that month.

Battle honours include Caen, Falaise, clearing the Channel ports, the Breskens pocket, and the final offensives of 1945.

During the Battle of the Scheldt, the 3rd Canadian Infantry Division had the nickname of "Water Rats" bestowed upon them by Field Marshal Sir Bernard Montgomery, commanding 21st Army Group, in recognition of the poor conditions of terrain through which they fought, first in the Normandy landings, and then in the flooded Breskens Pocket.

[6] By noon, the entire division was ashore and leading elements had pushed several kilometres inland to seize bridges over the Seulles.

A 1st Hussars armoured troop reached its objective along with men of The Queen's Own Rifles of Canada before nightfall, when both units moved 15 km inland and crossed the Caen-Bayeux highway.

Over the course of five days, the 12th SS launched a series of counter-attacks in an attempt to crush the Canadian bridgehead and throw them back into the sea.

The attacks cost the 12th a third of their armoured strength and they were forced to retire in the face of stubborn resistance, Allied naval gunfire and aerial superiority.

On 8 July, the 3rd Canadian Division participated in Operation Charnwood, the British Second Army's final advance on the northern parts of Caen.

The 3rd Canadian Division continued the advance on the 20th and the lead units came under heavy machine-gun and small arms fire from a chateau close to Colombelles.

The Queen's Own Rifles of Canada, with support from the 17th Duke of York's Royal Canadian Hussars, pushed forward once again despite heavy casualties and captured the heavily fortified village of Gibberville.

The German Panzer divisions in the area had been bled completely dry, losing a staggering number of tanks and men, which could not be easily replaced.

The 3rd Canadian Division and the other units involved in the offensive were allowed to catch their breath and they dug in, expecting a German counter-attack which never came.

On 5 September, 3rd Canadian overran the Fortress of Mimoyecques, revealing the infrastructure for the unknown V-3 cannon destroyed by the Tallboy bombs in July.

The formation was formed on the organizational structure of a standard infantry division and supplied units as part of Canada's commitment to postwar European reconstruction.

LFWA contributed extensively to domestic operations at home, and on missions abroad in locales such as the Balkans and Afghanistan for over two decades.

Battalions were represented by a series of coloured geometric patches that corresponded to their seniority within the brigades of the overseas divisions of the corps.

In May 1917, the commander of the 3rd Division published a routine order stating that, because the black patches were too difficult to see, French grey was to be worn instead.