Anachronisms: In the background of the shot showing the old crew tied up in the net is a luxury sealiner.
Continuity: When captain Vallo pulls a man overboard (at the beginning of the film), the man is wearing sailors' clothes, but when we see him fall into the water, he's wearing a uniform. Secondly, the man being pulled into the water is standing on the deck of the ship, but when we see him fall, he falls down from a mast.
Revealing mistakes: As the three heroes are carrying the upside down boat escorted by soldiers, it runs into a wall. The side of the boat wrinkles showing that it is actually made of fabric.
Continuity: When Vallo is giving orders to fire "port side battery" while in his guise as an "unmarried girl of the island" you can clearly see that he is wearing a bra. Later, when he and Ojo "strip for action" they're only wearing blouses.
Revealing mistakes: When Vallo and Ojo fly to the pirate ship in the hot air balloon, you can see the rope controlling the balloon as they jump into the rigging of the ship.
Audio/visual unsynchronized: During the party at the St Theo Garrison in honor of Baron Gruda/Vallo, when the dancers and singers enter, the audio and video are mismatched as Vallo whispers to Ojo, "Bertha, that dame we held for ransom."
Audio/visual unsynchronized: When Bertha shouts at the party, "It's the Crimson Pirate!" her voice and her mouth movements clearly don't match.
Continuity: When Humble Bellows is lowered over the side to listen to Captain Vallo speaking to Consuelo about his releasing her and her father, Humble is hanging upside down. When we next see Humble up on deck, he is soaking wet. Why drop him in the water, when deck side in only a body length and a hand up away?
Crew or equipment visible: While fleeing from the soldiers to establish themselves as rebels, after the hidden trampoline jump from one building to another, the light source in the last window obviously changes.
Continuity: Vallo wears red trousers when he is captured and abandoned with Ojo and the professor to the sea. In the little boat he suddenly wears gray trousers. (minute 61/63)
Continuity: As noted in an earlier Goof, the man pulled overboard near the start of the film is wearing a striped sailor's outfit on deck, but the shot of him falling into the sea shows a man in a soldier's uniform. That shot was intercut from the climactic battle scene at the end, when the same soldier is seen being knocked off the ship's deck, and the shot of him falling into the ocean is repeated.
Continuity: In several scenes throughout the film, Burt Lancaster's tan appears and disappears, varying between those shots filmed on location in the Mediterranean and ones later filmed in the studio in Britain.
Continuity: In the final fight, near the end of the film (1h, 39m, 30s), Ojo falls onto some enemies (and gets a barely seen bump on his back). Less than 3 minutes later, the same shot (about 1 second long) is repeated.