page_title: Y Sap mine
section_title: 1915
hierarchical_section_title: Y Sap mine / Background / 1915
caption_attribution_description: English: Chalk areas
context_page_description: 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.
context_section_description: Fighting continued in no man's land at the west end of La Boisselle, where the opposing lines were 200 yd (180 m) apart, even during lulls along the rest of the Somme front. On the night of 8/9 March, a German sapper inadvertently broke into French mine gallery, which he found to have been charged with explosives; a group of volunteers took 45 minutes to dismantle the charge and cut the firing cables. From April 1915 – January 1916, 61 mines were sprung around L'îlot, some loaded with 20–25 long tons; 44,000–55,000 lb (20,000–25,000 kg) of explosives.
  At the end of July 1915, fresh troops were observed moving into the French positions north of the Somme and on 1 August, they were identified at Thiepval Wood as British soldiers ("dressed in brown suits"). The British had formed the 178th and 179th Tunnelling companies in August, followed by the 185th and 252nd Tunnelling companies in October. Brigadier-General George Fowke the Engineer-in-Chief of the BEF, moved the 174th and 183rd Tunnelling Companies into the area but at first the British did not have enough miners to take over the large number of French shafts; the problem was temporarily solved when the French agreed to leave their engineers behind for several weeks. On 24 July, the 174th Tunnelling Company established headquarters at Bray, taking over some 66 shafts at Carnoy, Fricourt, Maricourt and La Boisselle. No man's land just south-west of La Boisselle was very narrow, at one point about 50 yd (46 m) wide, and had become pockmarked by many chalk craters.
  Elaborate precautions were taken to preserve secrecy, since no continuous front line trench ran through the area opposite the west end of La Boisselle and the British front line. The L'îlot site was defended by posts near the mine shafts. The underground war continued with offensive mining to destroy opposing strong points and defensive mining to destroy tunnels, which were 30–120 ft (9.1–36.6 m) long. Around La Boisselle, the Germans dug defensive transverse tunnels about 80 ft (24 m) long, parallel to the front line. On 19 November 1915, the 179th Tunnelling Company commander, Captain Henry Hance, estimated that the Germans were 15 yd (14 m) away and ordered the mine chamber to be loaded with 6,000 lb (2.7 long tons; 2,700 kg) of explosives, which was completed by midnight on 20/21 November. At 1:30 a.m. the Germans blew the charge, filling the remaining British tunnels with carbon monoxide. The right and left tunnels collapsed; it was later found that the German explosion had detonated the British mine.
caption: Map of chalk areas in northern France
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