SH3 Commander can cause some interesting things.
 

So I loaded up a new career in SH3 today and after doing the normal August training run I went onto the next patrol. Now I always use the randomize days spent in port option on Commander and never have I had such a short port stay. I had returned on the 5th of August and I was ordered out on the 14th! A 9 day turnaround doesn't seem all that likely especially given that IIRC war didn't seem likely to happen even at that late a date. I'm not complaining though as it just means i'll be in my corner of BF19 when the war does break out.

I also always use Random Days in Base except for my first patrol. I do a quick turnaround, set up my crew the way I want them and then set Commander for 18 Days in Base. This way my first real patrol will depart on the 19th, just as the original first war patrols did. After that all the downtimes are random.

You want a short turnaround? I once came back from an empty patrol in a Type II with all five torpedoes still on board. They had me out at sea again in just five days! I loved it. :sunny:

Well you can't say the boys in Wilhelmshaven are slackers.

Reading "Iron Coffins", Herbert Werner tells a story of many days and hardly any days off in port.
In the early war, boats could be off line and the crew at R&R for 21-28 days. Those with technical skills would be kept around to help overhaul the boat for its next patrol, but even they would get time off.
But by the time 1943-44 rolled around, well, parts and the trains to move them were in short supply, so it was repair what you can with available materials and then back to sea as fast as possible (even if the boat was barely capable).
What used to be a 28 day stay in port with the boat lovingly maintained, was now 5-10 days and chose your top 5 repairs (and be done quickly).
Made no sense to keep boats lounging around in port when you have no idea if or when the next trainload of repair parts is coming in. Might as well do something useful for the reich, get back to sea and sink something.
More often than not, it was the u-boat that never made it. By 1944, only 2 out of every 10 boats that went out came back. Depth charges were the least of their problems.