He also demonstrated courage under fire, visiting the front lines on numerous occasions at the height of battle and personally directing his forces in the face of poison gas attacks and heavy shellfire.

Mercer remains the most senior Canadian officer ever to die in combat and was unfortunate to be killed at the opening engagement of the largest battle of his career, when he was trapped by shellfire during a front line reconnaissance and overrun during the subsequent German attack.

Mercer was also a keen amateur painter himself and was also an excellent sportsman who represented Canada and the Canadian Militia in shooting contests both at home and in Britain.

Ordered to take his regiment to Camp Valcartier near Quebec City at 12.30 on 4 August, Mercer worked in his law office until 12.00 before arriving on time at the barracks in uniform.

[2] Within days he had been promoted to Temporary Brigadier-General in command of the 1st Canadian Infantry Brigade which consisted of the first four battalions of the Expeditionary Force recruited in Ontario.

"[5] Mercer's fellow brigadiers in the Expeditionary force, Richard Turner, VC and Arthur Currie commanded similar training camps and together the officers prepared their men for departure to France on 9 February 1915.

A German attack on French lines had caused massive casualties through the use of poison gas and Mercer's brigade was fed piecemeal into the battle as reinforcements by poorly coordinated staff officers.

[5] The next day, Mercer's men were directed to attack an escarpment named Mauser Ridge, an operation which failed because French troops ordered to support the Canadian line did not arrive.

Mercer himself travelled to the front line to witness the battle and came under fire for the first time before retiring in order to remonstrate with the French officers intended to support him.

[9] Byng ordered Mercer to make a reconnaissance of the front line and draw up a plan to overrun the more dangerous German positions in a local attack.

[9] The buried field hospital was also captured by the advancing Germans and as a result nobody who knew of the general's whereabouts on the day returned to Allied lines.

[5] Believing Mercer to have been captured, General Currie assumed command of the battle and with the use of saturation bombardment was able to retake the lost trenches and drive the Germans back to Mount Sorrel despite heavy casualties.

[5] On 21 June a Canadian burial party found 30 bodies in a sector of trench, amongst them General Mercer's remains, only recognisable by his uniform decoration.