DESCRIPTION. The German "KURT" apparatus is a spherical, hydrostatically operated, aircraft-laid, skip bomb; a copy of a similar device used by the British. It was designed to operate like a skipping stone over a smooth water surface for use against ship targets, power plants, lock gates, tidal installations and similar harbor facilities.

The information contained in this report was obtained through the interrogation of Ger-man scientists and prisoners of war. Complete specimens of this device have been ship-ped to the United States Navy Ordnance Investigation Laboratory.

Development of the "KURT" apparatus was commenced in the late 1943 at the German airforce experimental center (E-Stelle), Travemunde, Germany. The original model was a sphere approximately 30 inches in diameter and weighing 400-500 kg. It contained two fuzes; one, a type 59 fuze with a 23-second powder delay train, and the other, a hydro-static, type 44 fuze. The effective range of this spherical missile was calculated at 400 meters. To increase the range to 4,000 meters a rocket propulsion unit was fitted to the sphere. Some experiments were carried out with the propulsion unit but to actual test were made. Work was stopped on this device in August 1944 when efforts were directed to more advanced projects. Because of the scarcity of documents and test datum it is impossible to substantiate adequately the information obtained through interrogation.

The first experiments were carried out with a model having the same weight and dimen-sions as the final "KURT" warhead. The ideal altitude for the attacking plane was calcula-ted at 20 meters and at a speed of 700 km/h. It was found that under ideal conditions, the missile had an effective range of 400 meters. To increase the range and to offer more protection for the attacking aircraft, a rocket propulsion unit was added. The modi-fied "KURT" with rocket assistance included an air tail with its elevators preset to an angle of 10° to prevent sharp trajectory as in the case of the sphere without rocket as-sistance. (Because of the essentially shorter running distance of the sphere without rocket assistance, sharp trajectories and slight deviations from the target course were disregarded.) This modification proved unstable in flight because the assembly tended to rotate about its longitudinal axis, deviating from the target course to such an extent that the target would be missed completely. To obviate this large deviation and to give the missile directional stability, a gyroscope was istalled. However, no further tests were made.

DETAILS

A. Warhead:

Diameter: 750 mm.

The warhead, a spherical shell, is filled with cast hexanite and contains two fuze poc-kets. A transverse pocket, housing two KRUPP hydrostatic fuzes which replaced the type 50 fuze, runs thriugh the sphere and is open at both ends. The other pocket is set at an angle of 45° to the transverse pocket and contains a type 44 hydrostatic fuze.

B. Mid-Section. The cylindrical mid-section houses a gyro unit which is operated by a gas evolved from a burning element. It also houses the lifting lug and the explosive coupling which servers the warhead from the propulsion unit. (See fig. 19.)

C. Rocket Section. The rocket section is a steel cylinder 18 inches in diameter and 36 in-ches long. It houses the rocket propellant and 18 venturis. The weight of the propellant is approximately 90 kg.

D. Air Tail. The air tail is the same as used with the bomb-torpedo. It is made of ply-wood and its elevators are controlled by the gyro. Dimensions of the air tail: 18 by 36 by 50 inches. Total length of the KURT apparatus is 80 inches.

OPERATION

A. Without Rocket Propulsion:

Plane speed: 700 km/h.

B. With Rocket Propulsion:

Plane speed: 700 km/h.

C. The Range Depends On:

1. Height of plane.

Under ideal conditions the Germans considered the Kugel without propulsion 100 percent accurate at a range of 400 meters when dropped from an altitude of 20 meters at 700 km/h. If the missile was dropped from heights greater than 50 meters or at speed less than 700 km/h the effective range was decreased due to deviations from the target course. Rough waters also caused serious deflection which could not be controlled.

D. Fuze. In the original KURT without propulsion, two hydrostatic fuzes were used; a type 59 fuze that was designed to operate after a delay of 23 seconds, and a type 44 fuze designed to operate at a depth of 8 meters. The sphere was later modified to accommo-date two Krupp fuzes for normal hydrostatic operation at 8 meters, and an electrical time delay fuze in case the missile penetrated the ship's hull.

E. Condenser Fuze. A condenser fuze, ElAZ 49, functions in the following manner:

1. Ignites an explosive element which starts the gyro immediately upon release of the missile from the plane.

2. Ignites the rocket propellant by exploding a 1-kg black powder charge after a delay of 0.5 second.

3. Allows either one of two possible types of electric fuzes used, to be armed (electric hydrostatic or electric time delay).

4. Fires the explosive coupling after a delay of 4.5 seconds.

When the rocket propellant is ignited it burns from 3 to 4 seconds. One-half second after the rocket impulse ceases, the explosive coupling fires, severing the sphere from the after body. The rocket section drops off and the sphere continues toward the target. The missile then hits the target and sinks. When at a depth of 8 meters, one of the hy-drostatic fuzes is actauted to fire the main charge.

Figure 19 – SB 400 Skip Bomb (Kugel K - Kurt Apparatus)