A drillship is a maritime vessel that has been fitted with drilling apparatus. It is most often used for exploratory drilling of new oil or gas wells in deep water but can also be used for scientific drilling. It is often built on a modified tanker hull and outfitted with a dynamic positioning system to maintain its position over the well.
Drillships are able to drill in water depths of over 2000 meters.
In order to drill a Marine Riser is lowered to the seabed with a Blow Out Preventer (BOP) at the bottom.
Drillships are just one way to perform exploratory drilling. This function can also be performed by Semi-submersibles, jackups, barges, or platform rigs.
The first drillship was the Cuss 1.