This title intended as a spoof on the troubled MUTINY ON THE BOUNTY (1962) emerges as the odd one out in the "Carry On" series: not only do we only find just three regular performers here (Kenneth Williams, Charles Hawtrey and Jim Dale), but there's little typical material; taken on its merits, however, it isn't bad at all and not quite the dud described on the series' official website!
Incidentally, the irregular actors are the ones who score best particularly Bernard Cribbins as an unlikely but likable hero (his character is named Poop-Decker!) and Donald Houston, intense as the villain of the piece; on the feminine side, there's the surprise casting of Juliet Mills (as a floozie who passes off as a midshipman she sets out in search of her lost love, who turns out to be a pirate leader!). As I said, the "Carry On" stalwarts rather play second-fiddle here (especially Dale, who only gets an inconsequential bit early on), though Williams and Hawtrey manage to assert themselves during the film's latter half (when Houston and cohort Percy Herbert instigate a mutiny and our heroes are cast off at sea).
While there are obviously a number of laughs scattered throughout, the general tone is atypically serious: Williams playing the cowardly skipper of the "Venus", he's given the unsurprisingly ironic name of Captain Fearless even loses a leg and, consequently, gets twice the "desk job" he so craved for. Also in the cast is Cecil Parker as the long-suffering Admiral who sets the naïve, bumbling Cribbins off on a naval career and reappears at the end to decorate him and his companions (Houston has blackmailed Spanish Governor Patrick Cargill into yielding his entire fleet and is taking it victoriously back to England, when it's unwittingly destroyed by Cribbins & Co. the ship's loaded cannons go off during a deck-fire, with the deed being taken for a successful attempt on their part to repel the oncoming Spanish invasion!).