Another guided air-to-surface weapon in the arsenal of modern air forces is the guided anti-ship missile. The first such weapon was also developed (by Henschel) and deployed by the Nazi Luftwaffe. It was Hs 293 – a radio controlled glide bomb with a rocket engine slung underneath it.
Unlike Fritz X designed to be used against heavily armored targets, Hs 293 was intended to be used against merchant ships and lightly-armored vessels. This allowed the bomb to be used from a lower altitude and at an increased range compared to a gravity bomb such as Fritz X.
The weapon consisted of a modified standard 500 kilogram SC 500 bomb with an added “Kopfring” device on the nose for maritime use – to help ensure a relatively perpendicular axis of impact.
The bomb had a thin metal shell and a high explosive charge inside and was equipped with a rocket engine beneath its body, a pair of aileron-fitted wings, and the receiving FuG 230 component of the Kehl-Straßburg guidance and control system – the same as used in Fritz X gravity bomb.
Five colored 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.
A major drawback of Hs 293 was that after it 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 maneuver to evade attacking fighters without aborting the attack.
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, certain variants of the Fw 200 and the Do 217 used the Hs 293 operationally in combat.
Which was quite successful, actually. On August 25, 1943, an Hs 293 was used in the first successful attack by a guided missile, striking the sloop HMS Bideford; however, as the warhead did not detonate, the damage was minimal.
On August 27, the sinking of the British sloop HMS Egret 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 November 26, an Hs 293 sank the troop transport HMT Rohna killing over 1,000 personnel.
Although designed for use against ships, the missile was (unsuccessfully) used in Normandy in early August 1944 to attack bridges over the River See and River Selume. One bridge was slightly damaged for the loss of six of the attacking aircraft (due to heavy anti-aircraft fire and fighter cover).
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.
However, later Allied attempts at countermeasures were much more successful. British Navy 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.
This one worked, because the transmitter operator now did not have to try 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.
By the time of invasion of Normandy and the Southern France, the Allies developed even more efficient countermeasures. 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. Which made missile attacks all but futile.