Ruhrstahl X - 4 The Ruhrstahl X - 4 was a wire guided air - to - air missile designed by Germany during World War II . The X - 4 did not see operational service and thus was not proven in combat . The X - 4 was the basis for the development of experimental , ground - launched anti - tank missiles that became the basis for considerable post - war work around the world , including the Malkara missile . History . During 1943 , the USAAF ' s Eighth Air Force mounted a series of heavy raids against Germany . Despite disastrous 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 . A massive development effort resulted in a number of heavy - calibre 30mm autocannon designs like the long - barreled MK 103 and shorter barrel MK 108 cannon , and the even heavier - calibre 37 , 50 and 75 mm calibre " Bordkanonen " converted , auto - loading anti - tank and AFV weapons for use on twin - engined bomber destroyer s , air - to - air rocket s , SAM s and the X - 4 . Work on the X - 4 began in June 1943 , by Dr Max Kramer at Ruhrstahl . The idea was to build a missile with enough range to allow it to be fired from outside the range of the bombers ' guns ( what is now called a stand - off weapon ) , while being guided with enough accuracy to guarantee a " kill " . The X - 4 met these specifications and more ; its BMW 109 - 448 rocket motor accelerated the missile to over 1 , 150 km / h ( 715 mph ) - about the same speed as both the earlier Werfer - Granate 21 and folding - fin R4M rockets - and kept the X - 4 there during its " cruise " , between 1 . 5 and 4 km ( 0 . 9 - 2 . 5 mi ) , while the defensive guns had a maximum effective range of about 1000 m ( 1 , 094 yd ) . The rocket burned a hypergolic mixture of S - Stoff ( nitric acid with 5 % iron ( III ) chloride ) and R - Stoff ( an organic amine - mixture of 50 % dimethylaminobenzene and 50 % triethylamine called Tonka 250 ) as propellant , delivering thrust initially , declining to over the 17 - second burn . As there was no room for a fuel pump , the fuels were forced into the motor by pistons inside long tubes , the tubes being coiled ( as with a coil spring ) to fit inside the airframe . S - Stoff was so corrosive , it dissolved all base metals and was extremely difficult and dangerous to handle . The Germans planned to replace the motor with a solid fuel design as soon as possible . The missile was spin - stabilized at about 60 rpm , or one rotation a second . Thus any asymmetrical thrust from the engine or inaccuracies in the control surfaces would be evened out . Signals to operate control surfaces on the tail were sent via two wires , which unwound from bobbin s housed within long , bullet - shaped fairings , themselves mounted either on the roots of an opposing pair of the larger mid - body fins , or on those same fins ' opposing tips . A gyroscope kept track of " up " so that the control inputs from the pilot ' s joystick in the launch aircraft could be translated into yaw and pitch as the missile spun . Flares attached to two of the midsection wings were used to keep the missile visible through the smoke of its motor . The warhead consisted of a 20 kg ( 45 lb ) fragmentation device that had a lethal radius of about 25 feet ( 8 m ) . It was thought that the guidance system would allow the pilot to get the missile into this range in terms of pitch and yaw , but at the ranges that the missile could operate at it would be almost impossible to judge range to anywhere near this accuracy . For this reason the missile mounted a proximity fuze known as Kranich , an acoustical system that was tuned to the 200 Hz sound of the B - 17 ' s engines in cruise . The trigger range was . The first flight test occurred on August 11 , 1944 using a Focke - Wulf Fw 190 for the launch platform . Subsequent tests used the Junkers Ju 88 and Messerschmitt Me 262 , although they were not launched from the latter . The X - 4 had originally been intended for use by single - seat fighters , but the problems in guiding both the missile and the aircraft at the same time proved this to be unworkable . Instead the X - 4 was re - directed to multi - seat aircraft like the Ju 88 , while the R4M rocket was to be used on the single - seaters . The X - 4 was designed to be easily assembled by unskilled labour . It is possible some X - 4s were used in the closing weeks of World War II , although it was never delivered to the " Luftwaffe " . The fighter - interceptor designed to use this missile as its primary weapon was the Focke - Wulf Ta 183 Huckebein , which was just a " paper " and wind tunnel prototype . After the war , French engineers tried to develop a domestic version of the X - 4 , called AA - 10 . 200 units were manufactured between 1947 and 1950 . However , the program was disbanded due to the dangerous pre - flight refuelling involved ( the nitric acid and Tonka combination was highly explosive ) .