Focke Achgelis Fa 330 Bachstelze deployed from an U boat (c1942)

The FockeAchgelis Fa 330 Bachstelze (English: Wagtail) was a type of rotarywing kite, known as a rotor kite. They were towed behind German Uboats during World War II to allow a lookout to see further. The Fa 330 could be deployed to the deck of the submarine and was tethered to the Uboat by a 150 m (500 ft) cable. The airflow on the rotors as the boat motored along on the surface would spin them up. The kite would then be deployed behind the Uboat with its observerpilot aboard, raising him approximately 120 meters above the surface and allowing him to see much farther about 25 nautical miles (46 km), compared to the 5 nautical miles (9 km) visible from the conning tower of the Uboat As Allied air cover in other theatres of the war was considered too much of a threat, only Uboats operating in the far southern parts of the Atlantic and the Indian Ocean used the Fa 330. excerpts from an ARTE documentary