What was the type and country of th submarine?

It certainly appears to be a British T class submarine.

The gun platform as an extension forward of the conning tower was uncommon, most submarines having the guns placed on a mount on the deck. The Germans did modify four type VIIC boats to have special gun decks as part of the conning tower, but they had one gun forward, two guns aft of the structure.

The British A and T class boats both have the conning tower gun platform, each having a similar profile, but the shots in the movie from the bow of the boat makes it unlikely it was an A class boat - the T class has a very unique appearance.

While I can't be 100% certain, if you look at various pictures of WW2 British T class submarines, I believe you'll recognize them. Some images will make the bow bulge seem to be overly high, making the profile seem impossible, but if you see the pictures taken broadside from the submarine, it isn't as noticeable and seems to match what we saw in the movie.

What I"m not sure about is if it was a group 1, 2 or 3 T boat (slight but important differences) or the name of the boat that was used.