As with its immediate predecessor, the script for Carry on Jack started off as a non-Carry On film (originally entitled Up the Armada) and after a number of title changes was incorporated into the series.

Arriving to find the crew all celebrating as they are sailing tomorrow, he takes a sedan chair with no bottom (so he has to run), carried by a young man and his father to Dirty Dick's Tavern.

Poop-Decker wakes and dons a dress to cover his long johns, and downstairs, along with cess pit cleaner Walter Sweetly, is kidnapped by a press gang run by the Venus's First Officer Lieutenant Jonathan Howett and his bosun, Mr. Angel.

Now in charge of the ship, Howett and Angel sail for Cádiz and plan on taking it from Don Luis, the Spanish Governor.

They are successful, but their plot is ruined by Poop-Decker's group, who stumble into Cádiz (believing it to be Le Havre) and recapture the Venus.

In Cádiz, the former crew of the Venus are taken to be shot, but escape with five empty Spanish men-of-war to England for prize money and glory.

While Poop-Decker, Sally and Walter are working belowdecks on cutting off Fearless's infected leg, a fire gets out of control on deck and burns a sail, which sets off the Venus's primed cannons, hitting all five Spanish ships and thus once again thwarting Howett.

The overall plot in relation to Sally steals the idea from episode 2 of the British TV series Sir Francis Drake made three years earlier (1961).