Y Sap mine

The Y Sap mine was an underground explosive charge, secretly planted by the British during the First World War and ready for 1 July 1916, the first day on the Somme. The mine was dug by the Tunnelling Companies of the Royal Engineers under a German machine-gun nest known as Blinddarm in the front line, on the north side of the village of La Boisselle in the Somme département. The mine was named after Y Sap, the British trench from which the gallery was driven. It was one of 19 mines on the British sector to be blown at the start of the battle.

Y Sap mine was sprung at 7:28 a.m. on 1 July 1916 and left a large crater. The explosion of the Y Sap mine failed to assist the British attack as the German eavesdroppers at the Moritz 28 Nord listening station intercepted and passed on the British "good luck" message. The Germans removed machine-guns from the Blinddarm and at Zero Hour the machine-gunners caught the British infantry in crossfire. The 34th Division had the highest number of casualties of any of the divisions involved on 1 July. The crater of the Y Sap mine was filled in after World War I and is no longer visible.

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