When the Vulcan fires its torpedoes the bow changes to that of a WWII era submarine.
(At around 28:00) When radio operator Sparks is trying to hail the Vulcan submarine, he refers to the "S.S.N.R. Seaview". The commission plaques around the ship read "S.S.R.N. Seaview", so Sparks is using an incorrect call-sign.