page_title: 171st Tunnelling Company
section_title: Hill 60/Messines
hierarchical_section_title: 171st Tunnelling Company / Unit history / Hill 60/Messines
caption_attribution_description: English: Plan of the mine at La Petite Douve Farm, part of the mines placed by the tunnelling companies of the Royal Engineers in the Battle of Messines (1917). This drawing is based on the plans published in Roger Lampaert, De Mijnenoorlog in Vlaanderen 1914–1918, Roesbrugge/Belgium (Drukkerij Schoonaert) 1989.
context_page_description: The 171st Tunnelling Company was one of the tunnelling companies of the Royal Engineers created by the British Army during World War I. The tunnelling units were occupied in offensive and defensive mining involving the placing and maintaining of mines under enemy lines, as well as other underground work such as the construction of deep dugouts for troop accommodation, the digging of subways, saps, cable trenches and underground chambers for signals and medical services.
context_section_description: 171st Tunnelling Company was first employed in March 1915 in the Hill 60/Bluff areas at Ypres. The Germans held the top of Hill 60 from 16 December 1914 to 17 April 1915, when it was captured briefly by the British 5th Division after the explosion of five mines under the German lines by the Royal Engineers. The early underground war in the area had involved both the 171st and 172nd Tunnelling Company.
  In July 1915, 171st Tunnelling Company moved to Ploegsteert and commenced mining operations near St Yves at the southern end of the Messines ridge. The four deep mines at St Yves, charged with a combined load of 146,000 pounds (66,000 kg) of ammonal, formed part of the mine galleries that were dug by the British 171st, 175th, 250th, 1st Canadian, 3rd Canadian and 1st Australian Tunnelling companies as part of the prelude to the Battle of Messines (7–14 June 1917), while the British 183rd, 2nd Canadian and 2nd Australian Tunnelling companies built underground shelters in the Second Army area. 
  In December 1915, 171st Tunnelling Company began work on the deep mine at Trench 127 at St Yves. The mine consisted of two chambers (Trench 127 Left, Right) with a shared gallery. The name indicates the British lines where the initial shaft was dug, not where the mine was placed under the German positions. The shaft was completed to a depth of 25 metres (82 ft) within four weeks, however after driving a 310 metres (1,020 ft) gallery the Royal Engineers faced a sudden inrush of quicksand and a concrete dam had to be constructed. A new attempt was made, and by April 1916 the Trench 127 mine was ready, with the ammonal charges over 400 metres (1,300 ft) away from the initial shaft.
  At the end of January 1916, 171st Tunnelling Company began mining operations at La Petite Douve Farm. The farm, located next to the road from Messines to Ploegsteert Wood, was enclosed by a German trench system known as ULNA. Also at this point was a junction on the narrow gauge railway system which ran from the forward areas of Messines to the rear areas around Nieuwkerke. This operation was characterized by setbacks. Difficult geology lead to two mines being abandoned before completion, and after a charge of 23,000 kilograms (50,000 lb) of ammonal had been put in place beneath the farm, the gallery was discovered by a German counter-mining operation on 24 August 1916. Three days later the German miners blew a heavy charge, which shattered about 120 metres (400 ft) of the main gallery and killed four men engaged in repairs. This camouflet wrecked the British gallery completely and forced the Royal Engineers to abandon the tunnel, which then quickly flooded.
  At the end of February 1916, 171st Tunnelling Company began work on the deep mine at Trench 122 at St Yves. The mine consisted of two chambers (Trench 122 Left, Right) with a shared gallery. The name indicates the British lines where the initial shaft was dug, due west of where the crater is today. The area was dominated by a complex of German trenches and by mid-May first charge of 9,100 kilograms (20,000 lb) of ammonal was in place at Trench 122 Left. Another shaft (Trench 122 Right) was started part way along the original tunnel and after another 200 metres (660 ft), a charge of 40,000 lbs of ammonal was placed by the Royal Engineers beneath the ruins of Factory Farm which sat on the German front line.
  In April 1916, 171st Tunnelling Company moved to the Spanbroekmolen/Douve sector facing the Messines ridge. At Spanbroekmolen, 171st Tunnelling Company took over from 3rd Canadian Tunnelling Company and extended the work to the German lines, driving the tunnel forward by 523 metres (1,717 ft) in seven months until it was beneath the powerful German position. At the end of June 1916 the charge of 41,000 kilograms (91,000 lb) of ammonal in 1,820 waterproof tins was complete, the largest yet laid by the British. With the mine complete, the British selected two additional objectives to be attacked near Spanbroekmolen, Rag Point and Hop Point, which were 820 metres (2,700 ft) and 1,100 metres (3,500 ft) from th
caption: Plan of the deep mines at La Petite Douve Farm
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