The ‘Tail’ of the U-boat

Even while German U-boats ravaged Allied shipping through April 1943, the Germans refused to sit on their laurels and made numerous attempts to increase their tactical efficiency.

One of the great short comings of the U-boats, which sat very low in the water, was that their visual range — the distance they could spot Allied ships —  was limited to about 5 miles.

German technology could not produce a radar set small enough to fit on a submarine, so they developed a type of kite, known as a gyrocopter, to be mounted on the U-boat, making their lookouts taller.

The gyrocopter was the Focke-Achgelis Fa 330, named the Bachstelze (Wagtail), because it was to be towed behind a Type IX U-boat like a tail.

The unpowered Fa 330 was a very simple, small kite with three rotary wings made of metal tubing with a seat for the pilot and a small pedal-operated rudder. It was easily disassembled and carried in watertight containers behind a submarine’s conning tower.

In action, the Fa 330 was quickly assembled and attached to a winch and cable on the conning tower. As the U-boat plowed along the surface, the wind across the deck spun the three blades of the gyrocopter’s propeller and allowed it to lift off like a helicopter.

The gyrocopter did not require high speed — a wind of 10 mph across the deck would allow the Bachstelze to reach its maximum height of about 400 feet and gave the pilot, using binoculars, a visual range of about 25 miles. This allowed the sighting of a ship masts that were well below the curvature of the Earth when viewed from the submarine conning tower.

The pilot transmitted sighting information down to the submarine by telephone cable, and when the mission was over, the Fa 330 was winched back to the deck, disassembled and the submarine could submerge again.

The theory and practice of the towed Bachstelze was quite practical, except for one shortcoming: the time it took to recover the U-boat’s gyrocopter if the submarine was spotted and attacked by Allied aircraft.

When this happened and the U-boat had to crash dive, the tethering cable was jettisoned and the pilot was left to fend for himself. Standard procedure called for him to disconnect the blades revolving over his head with a quick release mechanism and then use a parachute to descend into the water safely. In theory, once the attack was over, the submarine would return and pick up the pilot.
More than 200 Bachstelze were built, but by the time they were ready for service in mid-1943, Allied aircraft were equipped with radar that made easy targets of German U-boats traveling on the surface.

The only places the Bachstelze was used successfully was in areas far away from Allied air power. It contributed to one confirmed sinking on Aug. 6, 1943, in the Indian Ocean off Madagascar and was carried on several submarines making cruises to the Far East. But there is no record of it contributing to any more sinkings.

In the end, the Bachstelze, though ingenious, proved to be another futile attempt by Germany to solve a problem the Allies solved with technology — in this case, miniature radar sets.

A number of Fa 330s survived the war and their unique role and small size have made them ideal museum display pieces. They can be seen at the Imperial War Museum in Duxford, England, the National Museum of the U.S. Air Force, and the Deutsches Technikmuseum in Berlin.

(Dr. Michel’s articles appear twice a month in the KA. For questions or comments, e-mail Dr. Michel at marshall.michel@spangdahlem.af.mil.)