Im going to look for a copy of it on DVD--after I get Cross of Iron on DVD.

I would say the top 4 Sub movies are and in my order of liking.

The Enemy Below.
Hunt For Red October.
U 571.
Das Boot.

For historical content, good portrayals of characters, excellent actors and scenery, and the "look" is correct as well.

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Lost are only those, who abandon themselves) Hans-Ulrich Rudel.