The German mining system at St Eloi was their most successful, but it still failed to detect the Canadian mine. The Germans had skilfully drained and consolidated the craters and found that they could sink inclined shafts from them owing to the clay being compacted by the force of the explosion. They succeeded in places in getting to 30m depth, which Füsslein likened to a torpedo net around a warship. In the spring of 1917 the Germans felt secure at St Eloi and in places had reached 40m depth and had galleries partly under the British positions. They had not, however, been able to sink shafts outside of the crater area and the Canadian gallery had bypassed much of their defensive system. Information from prisoners suggested to them that their blows had destroyed the British mining system. In fact, as in many places along the ridge, the British had already driven their deep mine before the Germans had themselves gone deep.²⁸