Aboard the latter was the helmsman and two operators for the radio control. Once under remote control, the crewless boats were directed towards the targets at 35 kt. The ultra-shortwave transmitter used for remote guidance was based on the earlier 1943 Borgward B-IV remote-controlled demolition vehicle. In addition, the boat operator switched on recognition lights of red and green that could only be observed from the stern before bailing out, so the command boat could properly align the boats with their targets. When the target was struck, a metal bumper framework around the bow was compressed, triggering a small charge that blew off the boats bow and also primed the fuse of the main, stern-mounted charge. The boats then sank and the 7 second delayed action charge detonated with the effect of a ground mine.

In September 1944 the construction program envisaged 1,200 units, of which all but 200 were to be radio-controlled, the remainder being wire-guided. At that time deliveries in August totaled 144 with 281 planned for September. In service, the Kriegsmarine found the original Series 1 boats, of light spruce construction, too flimsy for open sea use and later built an improved and strengthened version of their own.

Plans for rescue versions for Neger mini-sub operators and smoke-screen generating Linse defenders came to nothing as the boats were too dangerous to operate effectively and the losses incurred by their rare use did not justify further operations.

German operators of these craft referred to their duties as “Opferkämpfer” or “Suicidal missions”.