They're mentioned in the loading screen and you can call for them, but as Jander said, maybe there not out there till around '42.

If it's implemented, then its model, should be stored somewhere in the Silent Hunter 5\Data\Submarine folder

Refuel at sea should be implemented but probably it's not 3D realtime: ie. you reach a certain area, a screen/message is showed and that's all.

Wikipedia states that U-459 was commissioned 15 November 1941. Nothing about first patrol though.

http://en.wikipedia.org/wiki/U-459

Resupplying at sea works.
There are Resupply Map Locations defined in some of the campaign projects, I didn't see any in the Total Germany 39 campaign but there were some in Operation Drumbeat.

How it works is, if you are in the range of the resupply location, which can be defined using the Mission Editor, you call for a resupply using your radio guy. He will give you coordinates to the rendezvous point. You'll meet with the assigned ship/submarine (again the class of ship can be defined) and the icon to refit/resupply will show up when you are about a few km out..

I tried this by creating 2 resupply locations in the Baltic, my VIIB (!) supply boat showed up as planned.. I waited a few days to see if he disappears but after 3 days he was still there..

There also seems to be a minimum time between refits, because I kept getting denied at my 2nd resupply location..

What about the precursor to Supply U-Boats, Supply Surface Vessels. The dissapearance of the later in the Atlantic led to the introduction of the former to take over the role. The last effort to supply Atlantic U-Boats by surface vessels ended in Dec/1941, with loss of auxialiary cruiser "Atlantis" and supply vessel "Python".

U-459 was the first operational "Milkcow", it's first mission 21.03.42-15.05.1942, KM Grid CC, supplying U-108, U-333, U-564, U-98, U-571, U-582, U-352, U-566, U-69, U-594, U-572, U-558, U-751, U-103 and U-753.

Edit: Just read your post piri, so the player has to edit the mission/campaign files for optional resupply? Since there seems to be no graphical representation, i take it resupplying is instant?

Yes it's instant, similar to refits in ports. (Didn't check the time, not sure if it took some amount of hours)

The player doesn't have to edit the mission files, they're already defined at certain locations, in some of the campaigns. How historical I don't know, a campaign mod will surely rearrange these in the future..

The US campaign (drumbeat) seems to be the only campaign with resupple built into the game, as above you call for the resupply and a ship shows up close to refit you.

But and I don't know if this is a bug or not you can only resupple once in every patrol, which is a bugger because it's a long trip from the US coast to lorient

Type 7 taking part on op drumbeat?
isn´t that a bit strange, immersion killer, out of place AND unhistorical? :hmmm:

While Type VII's didn't take part in Operation Drumbeat proper, they did indeed operate off the U.S. east coast, the Gulf of Mexico and into the Caribbean.

well the crew are talking about new boat (but I haven't changed boat) confusing it's a long boring campaign guys, have to sink 300,000 tonnes