Hello Thomas,

you mean the U-Boat 511. A Large seo going Type IX. But the mentioned V2 was not more than some small rockets, fired from a very small ramp/. The Germany even had Poblems to start the V2 from land, so there even no need to think to start it from a U-Boat;-)

Here a text from uboat.net:

During the summer of 1942 the boat under the command of Kptlt. Steinhoff took part in some of the most interesting experiments of the entire world war. Steinhoff's brother, Dr. Erich Steinhoff was working at Peenemünde on the rockets program and they worked it out so that U-511 was used for rocket tests.

A rack for 6 30 cm rockets was installed and somewhat extensive tests were carried out. These were concluded with a successful launch of rockets from a depth of 12 meters. These amazing tests did not convince Dönitz' staff of their merit and they were not carried out. The rockets in question, the 30cm Wurfkörper 42 Spreng, was by no means advanced enough to target ships but it might have been used to bombard shore installations such as oil refineries in the Caribbean. That idea was born in late 1944 when type XXI boats were to tow V-2 launchers which would attack shore bases. The launchers, nor the XXI boats, were not available in time though.

Greetings Philipp