In the oeuvre of John Ford his late silents are ahead of his early talkies in artistic aesthetics because of two important factors: actors and dialogue. While he is most known for his sagacious later period films like The Searchers or The Quiet Man (and many others) he has several excellent 20s films like 3 Bad Men and Four Sons (I still have not seen Iron Horse which I will have to rectify soon). Those silents work quite well on a visual level and have a surprising amount of movement sometimes analogous to a Murnau film. When sound became prominent many producers felt forced to exploit this aspect which slowed down movement, placed people in specific positions due to microphones and forced the focus to be more on verbal acting ability. The latter was the rub in Ford's early talkies.
The biggest strength of this film is the look and feel of the settings and several nice shots of the camera. One of the biggest surprises is that most of this film is shot on location. There are beautiful shots on ships, on the sea and even some quick underwater shots (the earliest in a film I can think of) which show a submarine breaking the surface of the sea. John had the American naval at his disposal and it really showed. Given there is a possible anachronism of some of the equipment since this movie was supposed to take place during WWI.
Then there is the rub. The sound is typical of early 30s with very little music, stifled acting with hammy delivery and a general slow plot.
During WWI, a navel command is sending out a three-masted schooner in Spanish waters as a decoy (with a big hidden gun) to lure a famous U-Boat out of the water so it can possibly be torpedoed by a hidden American sub. When the navy personnel go ashore as merchants the captain falls in love with a double agent, while another personnel gets Mickeyed (sleeping potion) and left behind when the personnel cannot find him. The plot is mostly straightforward and the ending is obvious though still exciting. The Germans are treated (like in Grand Illusion) as humans so I do not think this played much in the 1940s.
An interesting movie that will be fun for people who enjoy 1930s films as long as they can handle some of the flaws of plot and acting. John Ford's use of camera is quite evident but does not quite handle the plot and characters as well as in his later films.
This movie can be found in the huge Fox at Ford box set.