Henschel Hs 293
The Henschel Hs 293 was a World War II German radio-guided glide bomb with a rocket engine slung underneath it that boosted the bomb in front of the launching bomber, to make it more visible to the weapons officer. It is the first operational anti-shipping missile, first used unsuccessfully on 25 August 1943 and then with increasing success over the next year, ultimately damaging or sinking at least 25 ships. Allied efforts to jam the radio control link were increasingly successful despite German efforts to counter them. The weapon remained in use through 1944 when  it was also used as an air-to-ground weapon to attack bridges to prevent the Allied breakout after D-Day, but proved almost useless in this role. Development. The Hs 293 project was started in 1940, based on the "Gustav Schwartz Propellerwerke" pure glide bomb that was designed in 1939. The Schwartz design did not have a terminal guidance system; instead, it used an autopilot to maintain a straight course. It was intended to be launched from a bomber at sufficient distance to keep the aircraft out of range of anti-aircraft fire. A Henschel team, under Dr. Herbert  Wagner, developed it the following year by adding a Walter HWK 109-507 rocket engine underneath, providing thrust for ten seconds. This allowed the bomb to be used from a lower altitude and at an increased range. Some examples used the BMW 109-511 of thrust. The first flight attempts took place between May and September 1940, with unpowered drops from Heinkel He 111 medium bombers used as carrier aircraft; the first Walter rocket motor-powered tests had been conducted by the end of 1940. The weapon consisted of a modified standard 500 kilogram "Sprengbombe-Cylindrisch"-class SC 500 "general purpose  bomb with an added Kopfring" on the nose for maritime use, to help ensure a relatively perpendicular axis of impact, with a thin metal shell and a high explosive charge inside, equipped with a rocket engine beneath the bomb, a pair of aileron-fitted wings, and the receiving FuG 230 component of the "Kehl-Straßburg" MCLOS guidance and control system, shared with the contemporary Fritz X gravity-propulsion, pioneering PGM armor-piercing bomb. The elevator was operated with an electrically powered jackscrew as the only proportional control, while the ailerons were operated with solenoids. Remote flight control was provided through  the "Kehl-Straßburg" link, with the Hs 293's control setup having no movable rudder on the ventral tailfin. The 109-507 monopropellant booster rocket provided for only a short burst of speed making range dependent on the height of launch. The Hs 293 was intended to destroy unarmoured ships, unlike the unpowered, armour-piercing Fritz X, which used the same "Kehl-Straßburg" system. Five coloured flares were attached to the rear of the weapon to make it visible at a distance to the operator. During night operations flashing lights instead of flares were used. After the missile was launched , the bomber had to fly in a straight and level path at a set altitude and speed parallel to the target so as to be able to maintain a slant line of sight and could not manoeuvre to evade attacking fighters without aborting the attack. Electronic countermeasures. The Allies put considerable effort into developing devices which jammed the radio link between "Kehl" transmitter and "Straßburg" receiver. Jammers aboard U.S. Navy destroyer escorts were ineffective at first, as the frequencies selected for jamming were incorrect. On balance, the probability that a Hs 293 launched (and seen as responding to operator guidance ) would actually strike a target (or achieve a damage-inflicting near-miss) was about the same at the Battle of Anzio as it was during Operation Avalanche. As attacks were taking place at Anzio, the United Kingdom began to deploy its Type 650 transmitter which employed a different approach to interfering with the FuG 203/230 radio link, by jamming the "Straßburg" receiver's intermediate frequency section, which operated at a 3 MHz frequency and appears to have been quite successful, especially because the operator did not have to attempt to find which of the eighteen selected "Kehl-Straßburg" command frequencies  were in use and then manually tune the jamming transmitter to one of them. The Type 650 automatically defeated the receiver, regardless which radio frequency had been selected for a missile. Following several intelligence coups, including a capture of an intact Hs 293 at Anzio and recovery of important components of the "Kehl" transmitter from a crashed Heinkel He 177 on Corsica, the Allies were able to develop far more effective countermeasures, in time for the invasion of Normandy and Operation Dragoon. These included AIL's Type MAS jammer, which employed sophisticated signals to defeat the Kehl transmission and to  take over command of the Hs 293, steering it into the sea via a sequence of right-turn commands. In contrast to the experience at Anzio, the jammers seemed to have had a major impact on operations after April 1944, with significant degradation observed in the probability that a Hs 293 missile could achieve a hit or damage-causing near miss. To improve control of the weapon and reduce vulnerability of the launching aircraft, wire-guided Hs 293B and television-guided Hs 293D variants were planned; neither was operational before the war ended. There was also a tailless delta winged  Hs 293F. In addition, there was a Hs 293H air-to-air model. Over 1,000 were built, from 1942 onwards. The closest Allied weapon system in function and purpose to the Hs 293 series was the US Navy's Bat unpowered, autonomously radar-guided unit. Later developments. The Hs 293 also served as the basis for a number of developments, none completed. These included the Hs 294, "designed specifically to penetrate the water and strike a ship below the waterline", with a long, conical shaped forebody and a pair of the Hs 293A's standard Walter HWK 109-507 booster  engines at the wing roots; the Hs 295, with longer fuselage, larger warhead and Hs 294 wings; the Hs 296, with Hs 294 afterparts, Hs 295 warhead and Hs 293 "Kehl-Straßurg" MCLOS control systems. Operational history. On 25 August 1943, an Hs 293 was used in the first successful attack by a guided missile, striking the sloop ; however, as the warhead did not detonate, the damage was minimal. On 27 August, the sinking of the British sloop by a squadron of 18 Dornier Do 217 carrying Hs 293s led to anti-U-boat patrols in the Bay of Biscay  being temporarily suspended. On 26 November, an Hs 293 sank the troop transport killing over 1,000 personnel. Other ships sunk or damaged by the Hs 293 include: Although designed for use against ships, it was also used in Normandy in early August 1944 to attack bridges over the Sée and Sélune rivers. One bridge was slightly damaged for the loss of six of the attacking aircraft. The attack on 7 August 1944 at Pontaubault, performed by Do 217 of III./KG 100, was the first usage of a standoff missile against a land target. On 12 April 1945 Hs 293A bombs  were used once more, against bridges on the Oder, by Do 217 bombers of KG 200. The Hs 293 was carried on Heinkel He 111, Heinkel He 177, Focke-Wulf Fw 200, and Dornier Do 217 planes. However, only the He 177 (of I and II."Gruppen"/KG 40), certain variants of the Fw 200 (of III./KG 40) and the Do 217 (of II./KG 100 and III./KG 100) used the Hs 293 operationally in combat.