The part of the U-Boat was played by a Venezuelan submarine, the former USS Tilefish (SS-307). The floating crane was, itself, a former WW2 tank landing craft.
The airplane itself, a Grumman Duck, that was used in the movie and flown by Frank Tallman, can now be seen on static display at US Air Force Museum in Dayton, Ohio.
This movie's title "Murphy' War" is a play on words of the epigram (or adage) "Murphy's Law" that says, "Anything that can go wrong will go wrong."