was considered impassable by tanks and most other military vehicles because of features such as salt lakes, high cliffs and/or escarpments, and fech fech (very fine powdered sand). The cliffs in particular acted as an edge of the El Alamein battlefield, which meant the British Empire's forces could not be outflanked to the south. Both Axis and Allied forces built their defences in a line from the Mediterranean Sea to the Qattara Depression. These defences became known as the Devil's gardens, and they are for the most part still there, especially the extensive minefields. No large army units entered the Depression, although German Afrika Korps patrols and the British Long Range Desert Group did operate in the area, since these small units had considerable experience in desert travel. The RAF's repair and salvage units (e.g. 58 RSU) used a route through the depression to salvage or recover aircraft that had landed or crashed in the Western desert away from the coastal plain. The RSUs included six-wheel-drive trucks, Coles cranes, and large trailers, and were particularly active from mid-1941 when Air Vice-Marshal G.G. Dawson arrived in Egypt to address the lack of serviceable aircraft. A German communications officer stationed in the depression was cited by Gordon Welchman as being unintentionally helpful in the breaking of the Enigma machine code, due to his regular transmissions stating there was "nothing to report". Qattara Depression Project The large size of the Qattara Depression and the fact that it falls to a depth of below mean sea level has led to several proposals to create a massive hydroelectric power project in northern Egypt rivalling that of the Aswan High Dam. This project is known as the Qattara Depression Project. The proposals call for a large canal or tunnel being excavated from the Qattara due north of depending on the route chosen to the Mediterranean Sea to bring seawater into the area. An alternative plan involved running a pipeline northeast to the freshwater Nile River at Rosetta. Water would flow into a series of water penstocks which would generate electricity by releasing the water at below sea level. Because the Qattara Depression is in a very hot dry region with very little cloud cover, the water released at the level would spread out from the release point across the basin and evaporate from solar influx. Because of evaporation, more water can flow into the depression, thus