They weren't expecting to find any survivors - but they did.
Video footage of a body retrieval mission on a shipwreck shows a diver's discovery of a man who survived three days in an air bubble.
"He's alive, he's alive!" the diver's shocked mission controller yells as a hand reaches out and clasps the glove of the submerged diver. "Hold him there, OK? Hold him there."
"F**** hell, I don't know what they're going to do," he mutters.
"Just keep him there, keep him calm, OK? Just reassure him, pat him on the shoulder," the controller says. "Just reassure him, give him a thumbs up, reassure him."
The cook had in the bathroom around 5am May 26 when the Jascon 4 tugboat started capsizing in heavy seas, around 20 miles off the Nigerian coast. It had been towing a Chevron oil tanker.
Unlike his 11 colleagues, who were locked in their rooms to keep safe from pirates, Harrison Okene was able to find an air pocket and wait for rescue.
He was trapped for more than three days, with no food or water.
Okene was dazed after being thrown from one end of the small cubicle to the other in the dark.
"As I was coming out of the toilet it was pitch black so we were trying to link our way out to the water tidal [exit hatch]," Okene told Reuters in June from his home town of Warri, a city in Nigeria's oil-producing Niger Delta.
"Three guys were in front of me and suddenly water rushed in full force. I saw the first one, the second one, the third one just washed away. I knew these guys were dead."
He groped his way into the engineers' office, took two mattresses from the beds and sat on top of them, hoping to stay afloat.
He could hear marine life swimming through the ship, and loud noises as fish started fighting over something - which he feared was his colleagues.
"I was very, very cold and it was black. I couldn't see anything," Okene said.
"But I could perceive the dead bodies of my crew were nearby. I could smell them. The fish came in and began eating the bodies. I could hear the sound. It was horror."
Okene said he heard the sounds of the hammer hitting the vessel May 28 and then Okene saw light from a head torch of someone swimming along passageway past the room.
"I went into the water and tapped him. I was waving my hands and he was shocked," Okene said.
The divers had been on a body recovery mission, not a rescue mission.
Okene had been underwater for so long, he had to be brought up slowly and put in a decompression chamber for 60 hours.
When he arrived to the surface, he thought he had only been trapped for 12 hours.