Hello Eric and Rainer,

I'd read something about it !
This device simulate a conning tower for been rammed by the destroyer and explose !
U-boat officers didn't want to use it cause of the bad maneuvrability and prefer to lost it !

In the same way,
Japaneses submarines used a big cargo container towed to supply the isolated garnisons !

Voilà,

Best regards

Ludovic.