It has varied quality miniature effects, with most close ups suffering from poor depth of focus.
Many shots are taken from much earlier films and exhibit an obvious grainy quality. There is a particularly odd over use of a totally out of focus miniature periscope shot.
Some shots appear to have been shot out at sea rather than in a tank as the horizon and sky look real, more than likely these have been lifted from "Action in the North Atlantic" from 1943.
Some of the underwater tank work, particularly the violence of the depth charges is well done while a few of the shots which I suspect were lifted from earlier films suffer from the overly clear pool water and obvious pool sides in the background.
Amusingly the sub sailors in the film are watching a sub movie complete with miniature shots of a submarine.
|Real horizon, not shot in a tank. Probably a shot lifted from "Action in the North Atlantic" 1943|
|Very grainy Stock shot from some other movie?|
|Pool sides easily apparent, underwater visibility way too clear.|
|Sailors in the movie watching a sub movie miniature shot from another movie.|
|The out of focus periscope shot that appears a number of times throughout the movie.|
|Animated search light beams, added in the optical printer and not too convincing.|