I'm writing a short story that involves the fate of a lost a WWI u-boat, specifically the Bremen, sister ship of the only other merchant u-boat, the Deutschland.

I'm definitely not an expert on submarines, so I need to get some help on technical details. I do have an engineering background so I reckon I can understand any answers y'all might give me (provided you use small words and a minimum of mil-spec acronyms :-)

The usual web sources all say the Bremen was lost enroute to Norfolk, Virginia in late 1916 or possibly early 1917, and that the area was likely somewhere south of Iceland. The reports are all pretty vague, and since U-53, her apparent escort for the voyage, reportedly received a transmission on 28 September 1916 that the Bremen was lost, the 1917 date seems pretty questionable to me.

What I need to know is if it would be possible for a u-boat of that era to be damaged to the point of being unable to manoeuvre, yet neither sink nor surface. Is there any plausible scenario where the Bremen could have been damaged in such a way as to trap her crew and eventually drift just under the surface for weeks or even months?

Assuming the entire crew die during or not long after the incident, would it be possible for a derelict Bremen to remain neutrally buoyant long enough to reach the Canary branch of the North Atlantic current? Or would something -- chlorine generated from acid spilling in the bilge, say -- inevitably cause a catastrophic change in buoyancy if unattended for that length of time?

Put another way, would a u-boat barely submerged but with no effective crew maintain depth, more or less, assuming she was not taking on water? I've read that at greater depths the pressure hull is compressed slightly making a neutrally buoyant sub unstable, but I don't know how much this applies to a sub at periscope depth, say.

With no crew to correct trim I would assume at minimum that the boat would not maintain even keel, but what else would happen to it?

Thanks for putting up with my naive questions, and I look forward to hearing back from you.

-Bobby