Complex sentence: Y Sap mine was sprung at on 1 July 1916 and left a large crater but failed to assist the British attack as the Germans had detected the mine in time and moved their machine-guns.
Split into simpler sentences: Y Sap mine was sprung at on 1 July 1916 and left a large crater. It failed to assist the British attack as the Germans had detected the mine in time and moved their machine-guns.