preparations for the battle, by placing 19 mines of varying sizes beneath the German positions along the front line and by preparing a series of shallow Russian saps from the British front line into no man's land. The saps would be opened at Zero Hour and allow the infantry to attack the German positions from a comparatively short distance. At La Boisselle, four mines were prepared by the Royal Engineers, charges No 2 straight and No 5 right were planted at at the end of galleries dug from Inch Street Trench by the 179th Tunnelling Company, intended to wreck German tunnels and create crater lips to block enfilade fire along no man's land. The Germans in La Boisselle had fortified the cellars of the ruined houses and cratered ground in the vicinity make a direct infantry assault on the village impossible. Y Sap and Lochnagar mines, named after the trenches from which they were dug, were excavated on the north-east and the south-east of La Boisselle, to assist the attack on either side of the German salient in the village. The 185th Tunnelling Company started work on Lochnagar on 11 November 1915. Two officers and sixteen sappers were killed on 4 February, when the Germans detonated a camouflet near the British three-level mine system, starting from Inch Street, La Boisselle, the deepest level being just above the water table at around . The diggings were handed over to 179th Tunnelling Company in March 1916. The Lochnagar mine consisted of two chambers with a shared access tunnel. The shaft was sunk in the communication trench called Lochnagar Street. After the Black Watch had arrived at La Boisselle at the end of July 1915, many fortifications, originally dug by the French, had been given Scottish names. The Lochnagar mine probably had the first deep incline shaft, which sloped from to a depth of about see map. The tunnel was begun behind the British front line and away from the German front line. Starting from the inclined shaft, about below ground, a gallery was driven towards the German lines. For silence, the tunnellers used bayonets with spliced handles and worked barefoot on a floor covered with sandbags. Flints were carefully prised out of the chalk and laid on the floor; if the bayonet was manipulated two-handed, an assistant caught the dislodged material. Spoil was placed in sandbags and passed hand-by-hand along a row