Komet weapons: BT1000 Bombentorpedo

Wenn Archive geöffnet werden, kommt manchmal Erstaunliches zutage: Jüngst wurden Hinweise auf eine Me-163 mit Torpedos gefunden.

In erst jetzt zugangigen Akten der ehemaligen Aerodynamischen Versuchsanstalt (AVA) Göttingen befanden sich eine Anzahl Aktenvermerke, die das Ausmessen eines Windkanalmodells der Messerschmitt Me-163B mit zwei untergehangten Bombentorpedos des Typs BT1000 beschreiben. In einer Aktennotiz über eine Besprechung zwischen einem Ingenieur Hubert (von Messerschmitt) und Professor Betz von der AVA wurde festgehalten, dass es dringend notwendig sei, den Einfluss der beiden angehängten BT1000 auf die Stabilität der Me-163 durch einen kurzen Windkanalversuch an dem vorhandenen Modell der Me-163B festzustellen. Der Aktenvermerk ist auf 9. Februar 1944 datiert. Der baldige Einsatz der Machine gegen Schiffsziele sei geplant und von den Messergebnissen abhängig. Die Messungen seien daher möglichst sofort nach Fertigstellung das Modells im Kanal durchzuführen. Das Modell sei Mitte Februar messfertig, die Messdauer betrage ein bis zwei tage, und eine längere Messreihe mit geringen Dringlichkeit sei daher zu unterbrechen. Unterzeichnet ist der Vermerk von einem Herrn Hildenbrand.

Weitere Aktennotizen sowie aufgefundene Fotos bestätigen, dass es tatsächlich Messreigen mit einem Me-163B-Modell mit unterhangten BT1000 Torpedos gegeben hat, auch wenn es heutzutage unsinnig erscheint, ein Flugzeug mit solch geringer Reichweite wie die Me-163 mit dieser Bewaffnung auszurüsten. In einem Schreiben der Junkers Flugzeug und Motorenwerke an die AVA vom 22 September 1944 ist die Rede von der Übernahme der Windkanal-Messungen an der Me-163B.

Bei den mit BT bezeichneten Abwurfkorpern handelte es sich um Entwicklungen der Forschungsanstalt Graf Zeppelin in Stuttgart-Ruit, die gegen Land- und Seeziele eingezetst werden konnten. Die Zahlenkennung hinter dem BT entsprach dem jeweiligen Gewicht. Der Abwurf der Sprengkorper sollte mit Hilfe eines eigens entwickelten Reflexviziers erfolgen, wobei die Wurfweite je nach Anflughohe bis zu 3000 m betrug. Den Antrieb lieferte ein Feststoff-Raketentriebwerk der Firma Rheinmetall.

When archives are opened, sometimes amazing news comes to light: eecently, references to a Me-163 with torpedoes were found.

In the files of the former Aerodynamic Research Center (AVA) Göttingen, which became only recently accessible to the public, there were a number of files describing the measurement of a wind tunnel model of Messerschmitt Me-163B loaded with two Bombentorpedos of the type BT1000. In a note on a meeting between an engineer named Hubert (von Messerschmitt) and professor Betz of the AVA, it was stated that it was urgently required that the effect of the two loaded BT1000s on the stability of the Me-163 was to be establised by means of a quick wind tunnel experiment. The file is dated 9 February 1944. The most rapid use of the machine against ship targets is planned and depends on the results of the measurements. The measurements should therefore be carried out in the wind tunnel as soon as possible after completion of the model. The model should be ready for use in the middle of February, the measurement period should be one to two days, and a longer series of measurements with little urgency should therefore be interrupted. Signed by a Mr Hildenbrand.

Further file notes and photos confirm that there actually was a Me-163B model with BT1000 torpedoes, even though it seems nonsensical today to equip an aircraft with such a range as the Me-163 with this armament. In a letter from the Junkers aircraft and engine works to the AVA of 22 September 1944 is a take-over of the wind tunnel measurements of the Me-163B is reported.

The BT-series of weapons were developments of the research institute Graf Zeppelin in Stuttgart-Ruit, which could be used against land and sea targets. The number identification behind the BT corresponded to the respective weight. The launching of the explosive devices should be carried out with the help of a specially developed reflex gun sight, the throwing distance being up to 3000 m depending on the approach height. The propulsion was supplied by a solid rocket engine from Rheinmetall.

BT (BOMBEN TORPEDO)

GENERAL. The aircraft torpedo is an expensive complicated weapon. The proportion of explosive weight is low. Mass production is lengthy and expensive. In addition present day performances of torpedo engines limit the speed and range of the projectile. Both of these items are essentials for accuracy and safety from antiaircraft fire.

A relatively simple weapon would result were the torpedo engine and the control gear omitted. If this simplified weapon were launched so that the greater portion of the distance to the target was covered through the air, as with an ordinary bomb, the initial speed of launch would be retained over nearly all the range. The projectile would enter the water just short of the target and carry on in the direction of its flight in air by reason of its momentum in the same way as does a torpedo. To prevent it from going too deep before detonation, a relatively flat angle of entry into the water is necessary.

Such a weapon was developed in Germany during the closing months of the war, and it was called the Bomben Torpedo. It combines the characteristics of the bomb to travel a long distance in a short time interval with the characteristics of a torpedo in that underwater travel eliminates range errors.

DETAILS. The BT was developed in four sizes: 200 kg, 400 kg, 700 kg, and the 1,400 kg. They all incorporated the same general shape and construction, and were entirely of steel. They were constructed in three pieces; the warhead (two sections) and the tail section. (See fig. 49.) The forward section of the warhead was in the shape of a truncated cone, and the after section of the warhead was cylindrical. The transverse fuze pocket was located in the cylindrical section just aft the point where the two sections were welded together. The suspension lug T-type, was secured to the warhead just forward of this weld at the center of gravity.

TAIL SECTION. The tail section was also in the shape of a truncated cone. There were three very large fins spaced 120° apart at the after end of the section. This type of tail provided excellent stability for the bomb while it was in the air. The tail section was secured to the after section of the warhead in such a manner that when the missile struck the water, it was jettisoned.

Early in the experiments, a BT 1000 was worked on and this missile had a rocket motor inside the tail section. This idea was soon dropped as it proved impractical for the missile.

FUZING SYSTEM. A magnetic fuze which reacts to the variable magnetic field of a ship is necessary for the most successful position of detonation under the keel of the ship. Work on this aspect of the bomb was found to be far from complete. The susceptibility to disturbances and the reaction capacity of such fuzes had not been investigated thoroughly either. A magnetic proximity fuze, however, is necessary for greater release ranges and for curved underwater trajectories.

Good detonation positions can be achieved with straight underwater travel if the fuze is set to go off after a specific distance through the water. The angle of entry must naturally not be altered as the underwater travel depends on the angle of entry. The time delay set on the fuze can be determined most simply by assuming a constant time for underwater travel.

In designing the fuze system, the following points must be borne in mind. An impact fuze with or without delay is required for direct hits on the ship. Further, the speed and range of release must be functioned very accurately for a pre-set time as the tolerance of plus or minus 0.1 second can only be achieved with a clockwork fuze. Finally, the tail section must be jettisoned by explosive bolts or by some other adequate method on impact with the water.

UNDERWATER BEHAVIOR. The bomb must in no event ricochet off the water not even in flat angles of entry, but must continue without deviation of its path of entry.

It is known that with ogival noses, as seen in the illustration of the BT 1400, a bomb will ricochet off the water when it strikes at a flat angle. By using a flat nose, as seen in the illustration of the BT 700, or better yet by using a spoiler plate, this ricochet at flat angles is definitely avoided. The frontal surface of the spoiler plate is made in the form of a section of a sphere of radius, equivalent to the distance between the surface of the spoiler plate and the bomb center of gravity. As the flow of force is practically perpendicular to the upper surface of the body when it is awash, the resulting flow of force must go through the center of gravity and thus it causes no turning moment.

A spoiler plate with the same diameter as the bomb however, has a high water drag. The ideal situation is to have the size of the plate less than the greatest caliber of the bomb body and so shaped that only the spoiler plate and no other part strikes the surface of the water at flat angles of entry.