The British dug six galleries under no man's land, placed large explosive charges under the German defences and blew them at 4:15 a.m. on 27 March.

On 16 April, the Royal Flying Corps (RFC) photographed the area, showing the Germans in craters 2, 3, 4 and 5 and a trench round the front lips.

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.

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.

The lowland west of the ridge was a mixture of meadow and fields, with high hedgerows dotted with trees, cut by streams and ditches emptying into the canals.

[2] January 1915 was a month of rain, snow and floods, made worse for both sides by artillery-fire, sniping and the need for constant trench repairs.

[7] In September, Brigadier-General George Fowke the Engineer in Chief, proposed a mining offensive in the blue clay 60–90 ft (18–27 m) underground.

[8] By January 1916, the 172nd Tunnelling Company had sunk shafts into the blue clay and began to dig galleries 80–120 ft (24–37 m) under the German front position.

Work was stopped on mine I, the furthest west, which was thought to be most vulnerable to exposure and on 10 March 1916, the Germans blew a camouflet which collapsed 20 ft (6.1 m) of the gallery.

On the afternoon of 26 March a listening post overheard British troops discussing mines to be fired at St Eloi but a careful inspection by German tunnellers found no cause for alarm.

[15] When the first shells passed overhead and the mines were fired at 4:15 a.m. on 27 March, it "appeared as if a long village was being lifted through flames into the air" and "there was an earth shake but no roar of explosion".

[16] The detonation obliterated the Mound and the trenches rocked and heaved, burying about 300 men of RJB 18, which had partly withdrawn into the reserve line as a precaution.

Infantry advanced quickly, ignoring the half-minute delay for flying débris and found that mines 2, 3, 4 and 5 had gone off under the German front and support lines, demolishing the defences.

Consolidation was slowed by the German artillery-fire; working and carrying parties of the 1st Royal Scots Fusiliers and the 12th West Yorkshires from the 9th Brigade had many casualties.

[14] A force from the 1st Gordon Highlanders, 12th West Yorkshire and the 3rd Division Grenade School staff was picked to capture the parts of the objective not taken during the attack on 27 March.

Haldane inspected part of the front, finding it waist deep in water and gave orders for another attack against crater 5 and the remaining objectives on 3 April.

The attack began after a hurricane bombardment from 1:30 to 2:00 a.m. on 3 April by the 8th King's Own in the dark and a thick fog and reached the objectives, finding the Germans unable to resist except at crater 5 and a party demanded their surrender at dawn at which 82 officers and men gave up, having been isolated and without food for three days.

The shallow ditches and captured trenches facing the wrong way had no drainage and few dugouts, all waterlogged and incapable of resisting shell-splinters.

The bombardment with artillery and trench mortars lasted for thirty minutes and destroyed much of the work of consolidation, the wire being swept away and two of four Lewis guns being knocked out.

[24] The British artillery began to barrage lines of approach and communication trenches but German infantry found ways through and broke into the centre of the Canadian position, where the defenders had been killed by the bombardment.

On 12 April, Plumer and Turner decided to concentrate on improving the front line; the frequent battalion reliefs were necessary due to fatigue and lack of sleep under constant bombardment, with no cover amidst mud and waterlogged shell holes.

During the night of 14/15 April, the 24th Canadian Battalion relieved the 25th and an officer crawled round the craters, reporting that the four along the old German front line were occupied.

On 16 April, the weather improved enough for air reconnaissance by the RFC and photographs showed that the Germans had dug a trench to the west of the craters.

[28] The mud and poor weather had imposed unprecedented misery on the infantry and after 19 April, a lull began and both sides were content to let the area quieten.

The British had attacked with a tired and depleted division and had not achieved all of the objectives, making a second attempt necessary, at the cost of foregoing a quick, thorough consolidation.

It was an open question as to the 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.

The fighting at St Eloi was one of nine sudden attacks for local gains made by the Germans or the British between the appointment of Sir Douglas Haig as commander in chief of the BEF and the beginning of the Battle of the Somme.

Since the French and British anticipated early advances in 1916, there seemed little point in improving defences, at a time when the Germans were building more elaborate fortifications, except at Verdun.

The British wartime volunteers gained experience in minor tactics but success usually came from machine-guns and the accuracy and quantity of artillery support, not individual skill and bravery; in the air the RFC overcame the Fokker Scourge and underground, the BEF tunnellers overtook the Germans in technology and ambition.

The brick plinth bears transparent plaques with details of the mining activities by the 172nd Tunnelling Company and an extract from the poem Trenches: St Eloi by the war poet Thomas Hulme (1883–1917).