The Lochnagar mine south of the village of La Boisselle in the Somme was an underground explosive charge, secretly planted by the British during the First World War, to be 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 field fortification known as (Swabian Height). A large crater has survived to the present day and is known as the Lochnagar crater or in French as Trou de mine de La Boisselle. The British named the mine after Lochnagar Street, the trench from which the gallery was driven. The charge at Lochnagar was one of 19 mines that were dug under the German lines on the British section of the Somme front, to assist the infantry advance at the start of the battle. The mine was sprung at on 1 July 1916 and left a crater deep and wide, which was captured and held by British troops. The attack on either flank was defeated by German small arms and artillery fire, except on the extreme right flank and just south of La Boisselle, north of the Lochnagar Crater. The crater has been preserved as a memorial and a religious service is held each 1 July. Background 1914 French and German military operations began on the Somme in September 1914. A German advance westwards towards Albert was stopped by the French at La Boisselle and attempts to resume offensive warfare in October failed. Both sides reduced their attacks to local operations or raids and began to fortify their remaining positions with underground works. On 18 December, the French captured the La Boisselle village cemetery at the west end of a German salient and established an advanced post only from the German front line. By 24 December, the French had forced the Germans back from the cemetery and the western area of La Boisselle but their advance was stopped a short distance forward at , in front of German trenches protected by barbed wire. Once the location of a farm and a small number of buildings, became known as (German, shell farm) to the Germans and later as the Glory Hole to the British. On Christmas Day 1914, French engineers sank the first mine shaft at La Boisselle. 1915 Fighting continued in no man's land at the west end of La Boisselle, where the opposing lines