several Führer Headquarters or FHQs located in various parts of Europe. The complex, built for Operation Barbarossa (the 1941 German invasion of the Soviet Union) was located in the Masurian woods, about 8 kilometres (5.0 mi) from Rastenburg, East Prussia (N/K/A Kętrzyn, Poland). Wotan – alternative name for the Y-Gerät radio navigation system. Würzburg radar – German air defense radar that went into service in 1940; over 3,000 of all variants were built. X X-Gerät – "X-device" or "X-equipment"; radio navigation equipment used on German aircraft. Y Y-Beam – German aircraft navigational system that utilized a single station that radiated a directional beam plus a ranging signal that the bomber picked up and re-transmitted to enable the ground controllers to compute the range and know when to order the bombs to be dropped. Y-Gerät – "Y-device" or "Y-equipment"; radio navigation equipment used on German aircraft. Z Z-Plan (or Plan-Z) was the name given to the re-equipment and expansion of the Kriegsmarine (Nazi German Navy) as ordered by Adolf Hitler on 27 January 1939. The plan called for 10 battleships, four aircraft carriers, three battlecruisers, eight heavy cruisers, 44 light cruisers, 68 destroyers and 249 U-boats by 1944 that was meant to challenge the naval power of the United Kingdom. The outbreak of World War II in September 1939 came far too early to implement the plan. Z3 – pioneering computer developed by Konrad Zuse in 1941, it was destroyed by bombardment in 1944. z.b.V. – see zur besonderen Verwendung. Zeit – time. Zeitplan – timetable, schedule. Zeltbahn – a triangular or square shelter quarter made of closely woven, water-repellent cotton duck. It could be used on its own as a poncho or put together with others to create shelters and tents. Also called Zeltplane. Zentralstelle II P – Central Office II P (Poland). Zerstörer – destroyer, also the designation for a Luftwaffe heavy fighter combat aircraft. Ziel – target, objective. Zimmerit – an anti-magnetic mine paste applied on the armour of German tanks to prevent magnetic mines from being attached. It was similar to cement, and was applied on the tanks with a rake, giving the vehicle a rough appearance. From the summer of the 1943 to mid-1944 Zimmerit became a standard characteristic on many German panzers. Zollgrenzschutz - (ZGS) Customs Border Guards. Zossen – The underground bunker complex that was headquarters for both the Wehrmacht (OKW) and (Heer) Army