HS-293

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The Germans were much more enthusiastic about the development of two other guided munitions, the Henschel “Hs-293A” and Ruhrstahl “Fritz-X” glide bombs. This section focuses on the Hs-293A, with the next discussing the Fritz-X.

The motivation for developing these guided weapons was attacks on naval vessels. Hitting a moving target like a ship from an aircraft is obviously much more difficult than hitting a fixed target on the ground. Of course, scoring a hit becomes easier the closer an aircraft gets to the ship, but as the saying goes: “If the enemy is in range, so are you.” The closer an aircraft got to a ship, the better a target it became for ship’s antiaircraft (AA) guns.

This problem was aggravated if the target was, for example, a heavily armored battleship. A conventional bomber had to attack such a monster from the air with armor-piercing bombs dropped from high altitude to give them the kinetic energy needed to punch through the target’s armor before exploding, but this made hitting the target difficult.

The alternate approach was the dive bomber, in which a pilot flew his aircraft flew directly down at the target at a steep angle, building up speed and ensuring accuracy through the simple measure of aiming his entire aircraft at the target, and releasing the bomb at low altitude. This put the dive bomber into the teeth of AA guns, and such aircraft also had to stand the stresses of screaming dives and the resulting high-gee pull-outs. That meant they could not be very big, and so in general could not have the long range needed for an ocean-patrol aircraft. Naval dive bombers were carrier aircraft, and the Germans never had an operational aircraft carrier.

Torpedo bombers had similar limitations. Dropping a torpedo from an aircraft was a somewhat tricky business, and it was difficult for an aircraft to carry a torpedo big enough to sink a large vessel with a few hits. Torpedo bombers were also vulnerable to AA fire while they made their torpedo drops. The skip bombing tactics used by the Americans in the South Pacific suffered some of the same drawbacks.

While dive, torpedo, and skip bombing were all used effectively by other nations, the Germans decided to pursue another option for antiship attack, one that would win out, decades later: guided weapons. Electronic guidance would allow the launch aircraft to release the weapon out of range of target defenses, and then direct it to a pinpoint strike on the target.

• A team at Henschel under Dr. Herbert Wagner began work on the Hs-293 in July 1940. Wagner and his team built a number of “Hs-293V-1” prototypes. These were unpowered glide bombs. They were tested successfully, and followed by a number of similar “Hs-293V-2” and “Hs-293V-3” prototypes, with minor refinements. However, the tests proved that an unpowered glide bomb tended to fall behind the launch aircraft, making it difficult to guide, and so the next version, the “Hs-293A-0”, had a pod strapped underneath its body containing a Walter 109-507B liquid-fuel rocket motor. Results were very satisfactory, and with a few further changes the weapon went into production as the “Hs-293A-1”.

The Hs-293A-1 was a radio-guided glide bomb with light alloy wings spanning three meters (ten feet) and tail surfaces of similar construction. While early units used conventional elevators and ailerons for control, production weapons used spoilers. There was no rudder; the bomb turned by banking.

The Walter rocket was powered by a fuel known as “Z-stoff”, which was a water-based solution of sodium permanganate or calcium permanganate, and an oxidizer known as “T-stoff”, or concentrated hydrogen peroxide — a fluid that is, incidentally, unstable, corrosive, and in general extremely nasty to handle. The Z-stoff was actually a catalyst that promoted the breakdown of the hydrogen peroxide into steam. The rocket motor could provide 5.9 kN (600 kg / 1,320 lb) of thrust for ten seconds. A flare was fitted to the tail of the Hs-293A to allow the operator to track its flight, after tests demonstrated it was hard to see the weapon at long range under conditions of poor visibility.

The warhead was based on the standard 500 kilogram (1,100 pound) SC500 high explosive bomb. Since the SC500 was not an armor-piercing bomb, the Hs-293A was intended for attacks on merchant vessels and other unarmored ships. The forward part of the Hs-293A’s fuselage consisted of the warhead, while the rear part contained the control electronics and batteries. The fuselage was 3.82 meters (12 feet 6 inches) long, and the entire weapon weighed 1,045 kilograms (2,300 pounds).

The production Hs-293A was controlled by the “Kehl-Strassburg” superheterodyne command and control system, with the Kehl transmitter unit in the launch aircraft and the Strassburg receiver system in the glide bomb. The bomb could be preset to one of 18 different frequencies in the 48:50 MHz band to allow up to 18 bombers to each drop and control a glide bomb simultaneously. The operator guided the bomb with a joystick wired to the Kehl transmitter. The first aircraft fitted to carry the Hs-293A was the Dornier Do 217. Eventually the weapon was also carried by the Heinkel He-111 or He-177, the Focke-Wulf? FW-200, and (in a pinch) by other types.

In operation, the carrier aircraft generally carried two Hs-293As?, one under each wing. Engine exhaust was piped into the bombs to keep the propellants from freezing. On release, the flare in the tail of the bomb and the booster rocket were ignited. The operator tracked the bomb by watching the tail flare, and used the Kehl unit’s joystick to keep the bomb lined up on the target. Depending on glide angle, the bomb could reach terminal velocities of 435 to 900 KPH (270 to 560 MPH). With release from an altitude of 1 kilometer (3,280 feet), the Hs-293A could glide as far as 11 kilometers (6.8 miles).