Hi Gilles, I assume you mean how long it took to get a boat ready to return to sea once it had returned. I would think there is no clear answer to this, although a boat may return undamaged, none or very few would I suspect would not need some kind of repair as to just get refuelled and supplied to be sent out again. That said, there are too many variables to take in to consideration.The age of boat, newer boats with less sea miles clocked up would require less general maintainence, while older boats especially those operating in the North Atlantic, with the storms and vast sea miles covered per patrol that they had to endure, then the general wear and tear would mean more parts in need of replacing or overhaul. also if any other structural problems had been noted during the patrol these too would effect the time spent in port. Even when the U-boats had returned to port, depending on how busy the port was, they may have had to wait their turns until a space was free. If you look at the u-boats patrols sections, noting the time each boat spent in port between patrols gives you an idea of the different periods each boat spent between patrols. Regards john