Need a Netflix membership to see it, but it's "instant watch" (no need to wait for a DVD), so even a preview membership lets you take a look.
ANYWAY, it's "The Log of the U-35" on this page:
World War I Films of the Silent Era
Obviously somewhat pieced together, but overall a very impressive production, given the period. I don't think I've seen motion picture of this many WW1-era subs, freighters, and warships anywhere else.