King of the Coral Sea (1954)

Ted King, aided by Jack Janiero, is in charge of a company owned by Peter Merriman, reputed playboy, which he inherited from his father. Merriman decides to have a look at the company which is getting shells and pearls from the ocean's bottom. King discovers a body out in the ocean and brings it in, which sets off a police investigation into the possible smuggling of undesirable aliens into the area and they ask for King's help. Merriman arrives and falls instantly for King's daughter, "Rusty." He also shows them that the use of modern equipment can streamline the operation as well as save lives, which he does for King when he is trapped under the sea. When the smugglers learn King is on their trail, they take "Rusty" hostage, but King, Jack and Merriman, with the use of Merriman's aqua-lungs, follow and rescue her and capture the crooks and killers before the police arrive.