27th. March 1916 Ypres indirection of Messines.

Second Army (Plumer)172nd Tunnelling Company, Royal Engineers
V Corps (Fanshawe) 
3rd Division
Canadian Corps (Alderson) 
2nd Canadian Division

St Eloi lies on the road running south from Ypres in the direction of Messines. Here, an awkward trench salient poked into British positions with the enemy on slightly higher ground - including an artificial earth bank called “The Mound” - that gave the Germans excellent observation over British trenches and roads. This had been the scene of almost continuous mine warfare during 1915, with both sides actively engaged. In all some 33 surface mines had been exploded within a small area, of which the Germans had fired the majority. British activity had been more on the defensive, with many camouflet charges being blown in an effort to destroy the enemy’s mine works. However, in summer 1915 three much deeper (60 feet) shafts had been started by the 172nd Tunnelling Company RE, which by now extended to six mines. The central four reached under the German trenches, the two on the outside were terminated under no man’s land, the idea being to create craters that would provide useful cover. Above ground, the churning by mine explosions and shellfire had created a very difficult terrain for infantry assault – added to which it was still waterlogged from the winter.

This map dates from Spring 1917 and shows German trenches (red) at that time. The numerous mine craters south of the village are clear enough. The craters formed by mine explosions on 27 March 1916 are those in the German front line.

Second Army commander Herbert Plumer decided that he must strike a retaliatory blow following the loss of the Bluff on 14 February 1916. Even while preparations were underway for an organised counter attack to recover the Bluff positions, orders were given to prepare too for action at St Eloi.