Ontario Farm was in the German lines and faced south covering the whole front looking towards Ploegsteert. This mine was the work of 171 Tunnelling Company. They sank the shaft behind Boyle’s Farm.
Two previous attempts had met with failure due to the ground conditions. On the 28 February 1917, just four weeks after starting the work, a ‘tubbed’, cylindrical steel sections used for sinking shafts in wet ground, shaft had been sunk 95 feet down to the level of the blue clay and this decreased in diameter as the shaft descended, not unlike a telescope.
When the drive had proceeded 100 yards a chamber was made and from this an interior shaft was created and went down 30 feet from where the drive continued. On reaching 540 feet and without warning water and sand came surging into the gallery. A dam was created but 100 feet of the gallery was lost. The 171 tunnellers had encountered a similar problem at the mine they had created at Trench 127.
On further investigation of the Belgian geological records they discovered that they had struck into an old glacial river bed. The gallery was branched to the left and inclined down however, there was also damage caused to the shaft head by German shelling and it appeared that the objective would not be reached. The Germans had not detected any underground work however, their suspicions were raised when the British overreacted with uncharacteristic heavy shelling to the Germans blowing anti-tank craters at Ontario Farm. Also, the water level changed after the craters had been blown which suggested to the Germans that they might have broken into a British gallery and the water drained off into this. The German mining officer wanted to blow a heavy mine from their shaft ( known as Gerhard) however, the divisional commander refused on the grounds that this might destroy the German concrete shelters in their defences.
By the end of May 1917 the British gallery was beneath the ruined buildings and by 6 June 1917, a day before zero, this had been chambered, tamped and charged with 60,000 lbs of ammonal and the leads connected. Lieutenants Percy Ellis and Henry Daniell took their places beside the two firing wires. At 103 feet below the surface this was the second deepest mine of all the Messines mines. When it was fired it did not create a crater. According to Grieve and Newman in their book ‘Tunnellers’ the Ontario Farm mine resembled a seething caldron. ‘For a long time after the blow the crater resembled a seething cauldron, the semi-liquid mud bubbling like some gigantic porridge pot on the boil.’
