The tunnellers developed counter tactics, which both sides deployed. The first was the use of large mines placed in one's own tunnels – some actually dug towards enemy noise to create damage – which when exploded would create fissures and cracks in the ground, making the ground either unsuitable for tunnelling or destroying existing tunnels and works. A small device, called the camouflet, created a localised underground chamber designed not to break the surface and form craters, but to destroy a strictly limited area of underground territory – and its occupants. The second tactic, deployed when the enemy tunnel was too close to your existing works or trenches, was the deployment of rod-fed torpedo shaped camouflet charges. Effectively land mines on the end of long iron sticks, the technique was a defensive tactic against an immediate threat. Towards the end of the tunnel war, forces also deployed mines at greater depths, which, coupled with the use of listening devices, could be exploded away from friendly trenches as a defensive measure. The British tunnellers had three advantages over their German counterparts, the Pioniere:  Firstly, the British used clay-kicking which was a virtually silent method of tunnelling. The Germans did not know of this technique, having not used it in their pre-war civil engineering, and thus used mattocks (a type of pick-axe) and other loud tools throughout the war. This made their tunnels more vulnerable to detection and attack. Secondly, the use of clay-kicking made the British four times as fast at tunnel digging as their German counterparts. Thirdly, British positions were most often located in low-lying areas, while German positions tended to be more elevated. Although this made the British more vulnerable to shelling, it also meant that British tunnellers had less of the soft quicksand-like 'Kemmel Sands' (known to the Germans as "Schwimmsande"), an integral component of the geological make-up of the ridges around Ieper (Ypres), to penetrate. While the bottom blue clay layer was virtually flat, as was the Kemmel Sands that sat on top of it, there was a dry strata which varied above this which created the geographical contours. This varying dry strata increased pressure on the Kemmel Sands, which unable to egress water below them, made them wet and unstable. When punctured, the Kemmel Sands would often "spout" under pressure, both water and solid material. Difficult to dig through and keep the mining wooden structure stable, the Germans, assuming that the British had the same instability problem, dug few tunnels until 1916.