Switched to GWX

[Ifernat]

Finally, I mysteriously died for no apparent reason.

Most of your other questions have been answered but I did want to elaborate on this. In all likelihood if you weren't running aground then the answer is you struck a mine, especially if you were off the East Coast of England (or in coastal waters) in mid 1940 or later.

GWX does a good job of simulating the ever increasing number and density of the British coastal minefields that were laid to protect coastal shipping. If you're on the surface (Or if you happen to be a heavy merchant with a 10m max draft) you'll go right over the top of them. A submerged U-boat at 15m depth however....boom.