Transocean Marianas was an Earl & Wright Sedco 700 design semi-submersible platform drilling unit capable of operating in harsh environments and water depths up to 7,000 feet (2,100 m) using a 47.6 cm (18.75 in), 15,000 psi blowout preventer (BOP), and a 53 cm (21 in) outside diameter (OD) marine riser.

[4] In 1988, as Tharos, the vessel operated by Occidental Consortium as a large firefighting, construction, diving support and accommodation vessel equipped with a helicopter and a hospital ship with 22 beds, that rescued survivors from the Piper Alpha oil platform disaster.

[5] The vessel carried out firefighting on the night of the disaster and supported the fire fighting and well kill operations that led to the extinguishing of the blaze.

Tharos's role in the early hours of the disaster was shown in the 1990 Scottish Television series Rescue.

On July 6, 2011, Transocean Marianas was evacuated due to taking on water off the coast of Ghana.