The huge action-filled concluding sequence in Thunderball. It was filmed in segments over a period of six days in the waters off Nassau, with sixty divers from Miami-based Ivan Tors Studios. One important sequence was filmed around a sunken US Navy landing craft, where Bond (Sean Connery) lures two SPECTRE frogmen to their deaths. The rest of the battle spread itself across the Nassau seascape.
Filming an underwater war was, at times, almost too realistic. In one scene, Bond flicks a switch on his trick backpack and fires an explosive spear at an enemy diver. In the actual sequence, Courtney Brown, portraying the SPECTRE diver, was given an explosive charge to place on the outside of his wet suit. When the spear was fired—on a line—it was designed to strike the charge and create an underwater explosion of black powder. Unfortunately, Brown placed the charge underneath his wet suit instead, so when the spear hit, it blew a hole right through the suit, severely burning his skin and landing him in Princess Margaret Hospital.
Bond’s jet-propelled diving backpack—designed by Jordan Klein—which gives him super underwater speed, was actually a nonfunctional prop. A piano wire attached to a speedboat propelled Bond’s double, Frank Cousins, through the water. If Cousins had turned his face at any moment, the force of being pulled at such speed would have torn the diver’s mask from his face.
Most of the battle took place in twenty feet of water off Nassau’s Clifton Pier. Into the battle, the producers threw every piece of equipment in the Thunderball arsenal, including the SPECTRE bomb sled, the scooters, and the scores of CO2 guns that sprayed a lethal underwater rain of spears among the fighting ranks, the free-swimming, orange-suited US Navy aqua-paras versus the black-suited underwater SPECTRE flotilla. Seemingly invincible behind their spear-firing sleds, Emilio Largo’s frogmen are systematically overwhelmed in hand-to-hand combat by Bond and his aqua-paras.
“The underwater sequences, especially the final battle, were too long,” recalled director Terence Young, who became disenchanted with Thunderball during its final weeks of shooting. “The trouble was that people kept wondering what the hell was going on. Of all the Bond films, Thunderball was the only one where the audience had at least a half hour of meditation during those long underwater sequences. People began to ask questions that we didn’t want them to ask until they were on their way home.
“I thought that the first underwater scenes were delightful, especially the opening sequence in which the Disco Volante sends out her divers to recover the hijacked atomic bombs. But in the later fight sequences, we kept repeating ourselves. There was nothing you could do except fire a spear at somebody, pull his mask off, or cut his lifeline. So when you’ve done that stuff forty-five times, the audience is naturally going to clamor for something new.”
 Terence Young, interview by Steven Jay Rubin, London, June 25, 1977.