Ruhrstahl X-4

The X-4 did not see operational service and thus was not proven in combat but inspired considerable post-war work around the world, and was the basis for the development of several ground-launched anti-tank missiles.

Despite heavy bomber losses, these prompted Luftwaffe research into considerably more powerful anti-bomber weaponry in order to reduce the cost in lost fighter aircraft and aircrew.

Signals to operate control surfaces on the tail were sent via two wires (a method chosen to avoid radio jamming),[4] which unwound from bobbins housed within long, bullet-shaped fairings, themselves mounted either on the roots of an opposing pair of the larger mid-body fins (there were four, swept 45°),[5] or on one pair of those same fins' opposing tips; these contained a total of about 5.5 km (3.4 mi; 3.0 nmi) of wire.

The X-4 had originally been intended for use by single-seat fighters (including the Me 262 and possibly the Dornier Do 335),[12] but the problems in guiding both the missile and the aircraft at the same time proved unworkable.

The X-4 was designed to be easily assembled by unskilled labour and airframe production began in early 1945 incorporating low-cost (non-strategic) materials, such as wood for fins.

[13] Production was hampered by Allied bombing of the BMW rocket engine factory at Stargard, though as many as 1,000 X-4s may have been completed,[14] the missile was never officially delivered to the Luftwaffe.

However, the program was disbanded due to the dangerous pre-flight refueling involved (the hypergolic nitric acid and Tonka combination was highly explosive).