This movie was made at a time when America did not let other countries push her around.
An excellent depiction of the challenges faced by merchant Marines. In fact, it could be argued that the merchant Marines had a tougher job than the Navy. The merchant Marine ships were either unarmed, or poorly armed, and had little ability to defend themselves. Their ships were more fragile and had thinner hulls.
I'm not a big stickler for historical accuracy in these dramas. In the beginning of World War II, the German U-boats refer to this as the "happy time". As the war progressed the United States and Great Britain became much better at defending their convoys. Sinking convoy ships in the second half of World War II was much more risky for the Germans thanks to naval escorts and aircraft escorts that both spotted and attacked German submarines.
There's a scene in the movie where a German submarine is chasing and catching up to a cargo ship. The German submarines were quite slow, and it's unlikely one could catch up to a merchant ship running at flank speed. Unless the merchant ship was somehow damaged and prevented from traveling at its maximum design speed. Typically, the Germans had to try to get in front of the convoys and do minimal maneuvering to set up their shots.
I have some experience traveling on the Atlantic Ocean. The most important piece of advice I can give you is only sale on a vessel flagged by the United States or Great Britain, (as opposed to some small third world country). These two countries have the world's best seamanship.
The acting is excellent. When not in action, the men spent most of their time talking about, and thinking about women. The special effects are very well done. This was accomplished mostly through the use of miniatures and models. Yes, if you look carefully you can see a wire pulling a submarine or a torpedo. I have no problem with these issues as the wonderful story portrayed in this movie does not require excellent special-effects. Although, the effects are well done.
I've never been completely comfortable with the word "propaganda". To me, propaganda involves lying. However, strictly speaking, propaganda can be telling the truth from a certain point of view. American filmmakers voluntarily made these types of movies to educate Americans about the enemy being faced. A controversial part in this movie is when the German submarine rams a lifeboat of survivors. I suspect this was not a typical activity, as once the Germans made a kill they would move on quickly. However, I have little doubt that it did happen on some occasions.