Two men who survived a US airstrike on a suspected drug smuggling boat in the Caribbean clung to the wreckage for an hour before they were killed in a second attack, according to a video of the episode shown to senators in Washington.

The men were shirtless, unarmed and carried no visible radio or other communications equipment. They also appeared to have no idea what had just hit them, or that the US military was weighing whether to finish them off, two sources familiar with the recording told Reuters.

The pair desperately tried to turn a severed section of the hull upright before they died. “The video follows them for about an hour as they tried to flip the boat back over. They couldn’t do it,” one source said.