Operations along the Vimy Ridge were accompanied by extensive underground excavations. The Arras–Vimy sector was conducive to tunnelling owing to the soft, porous yet extremely stable nature of the chalk underground. Underground warfare had been conducted on the Vimy sector since 1915. Bavarian engineers had blown twenty mines in the sector by March 1915. By early 1916, German miners had gained an advantage over their French counterparts. British tunnelling companies of the Royal Engineers took over progressively from the French between February and May 1916.