The Actions of St Eloi Craters from 27 March to 16 April 1916, were local operations in the Ypres Salient of Flanders, during the First World War by the German 4th Army and the British Second Army. Sint-Elooi (the French is commonly used in English) is a village about south of Ypres in Belgium. The British dug six galleries under no man's land, placed large explosive charges under the German defences and blew them at on 27 March. The 27th Division captured all but The 46th Reserve Division counter-attacked but the British captured on 30 March. The Canadian Corps took over, despite the disadvantage of relieving troops in action.
The Canadians inherited positions in a deplorable state, the British having pressed their advantage, rather than consolidating the captured ground. On the night of a German methodical attack () recovered the captured craters. Canadian runners struggled to deliver messages and for several days the Canadian and British staffs were ignorant of which craters had been captured, the topography having been changed so much by the mine detonations. There were the new ones superimposed on the old, the ground full of shell-holes and derelict trenches. Snipers made it impossible to orientate and fresh troops easily mistook one pair of craters for another.
The Canadians counter-attacked several times, then concentrated on consolidating the front line, ready for another attempt. Constant rain, oozing mud and incessant artillery-fire exhausted troops quickly and battalions had to be relieved after a couple of days. Canadian and British staffs were still ignorant of the German capture of Conflicting reports added to the uncertainty but a reconnaissance by a Canadian major on 10 April found that the Germans were in crater 4. On 16 April, the Royal Flying Corps (RFC) photographed the area, showing the Germans in and a trench round the front lips. Plans to attack were cancelled and for two weeks both sides exchanged artillery-fire.
The mud and poor weather caused unprecedented misery on the troops but the first attack showed that with preparation, surprise and good timing a limited objective could be captured. The British had attacked with tired troops and had not achieved all of their objectives and the second attempt was at the cost of quick consolidation. At St Eloi, against an attack on a narrow front, where the defender had good observation, the ground could not be held. It was an open question as to what width of front to attack, narrow enough to guarantee success, yet wide enough to force the Germans to disperse their artillery-fire so that captured ground could be held.
Background
Ypres district
Ypres lies at the junction of the Ypres–Comines Canal and the Ieperlee. The city is overlooked by Kemmel Hill in the south-west and from the east by low hills running south-west to north-east, with Wytschaete (Wijtschate), Hill 60 to the east of Verbrandenmolen, Hooge, Polygon Wood and Passchendaele (Passendale). The high point of the ridge is at Wytschaete, from Ypres, while at Hollebeke the ridge is distant and recedes to at Polygon Wood. Wytschaete is about above the plain; on the Ypres–Menin road at Hooge, the elevation is about and at Passchendaele. The rises are slight apart from the vicinity of Zonnebeke, which has a gradient of
From Hooge and to the east, the slope is near Hollebeke, it is heights are subtle but have the character of a saucer lip around Ypres. The main ridge has spurs sloping east and one is particularly noticeable at Wytschaete, which runs south-east to Messines (Mesen), with a gentle slope to the east and a to the west. Further south is the muddy valley of the Douve river, Ploegsteert Wood (Plugstreet to the British) and Hill 63. West of Messines Ridge is the parallel Wulverghem (Spanbroekmolen) Spur; the Oosttaverne Spur, also parallel, is to the east. The general aspect south of Ypres is of low ridges and dips, gradually flattening to the north into a featureless plain.
In 1914, Ypres had and inside medieval earth ramparts faced with brick and a ditch on the east and south sides. Possession of the higher ground to the south and east of the city, gives ample scope for ground observation, enfilade fire and converging artillery-fire. An occupier also has the advantage of artillery deployments and the movement of reinforcements and supplies being screened from view. The ridge had woods from Wytschaete to Zonnebeke, giving good cover, some being of notable size, like Polygon Wood and those later named Battle Wood, Shrewsbury Forest and Sanctuary Wood.