Carry on Jack was part of a whole series of British comedies back in the sixties (there was like 15 of these Carry on ___________). Beside this one, I've seen Cowboy, Cleo, and another one I can't remember. They are mostly done by the same group of actors, although this time, they had some new people I hadn't seen before. The humor in all of these is a bit dry (a British trademark, and one I appreciate) and littered with puns. The main character's last name is Poop-Decker, for example. The movie is set during the war between Spain and England, and deals with the navy. The main character finally graduates the academy, and gets a commission. Before he even gets aboard his ship, his identity/commission is stolen by a woman, and he gets press-ganged into serving on the ship he's supposed to be on.

Movies always expect a suspension of belief when a woman pretends to be a man. It's always blatantly obvious to the audience, yet none of the cast can figure it out. This is especially present in Far East films. A couple of times, I'm pretty sure the captain even checked her out while she was in drag. 

The captain was my favorite character. He always plays this type of character. He's named Captain Fearless, but he becomes sea sick, runs from battle, can't stand the sight of any kind of pain,etc. 

I gave the movie a 6 out of 10 (IMDB has it at a 5.9 right now).