Drillship
This type of drilling unit is more in line with a conventional ship than any of the others. Designed around the normal hull of a ship, complete with bridge etc, a drilling package is built into the ship, as can be seen by the tall drilling derrick on the Transocean's Discoverer Spirit left, along with all the associated additional equipment, pump rooms etc below decks within the hull.

Much more versatile than a Jack-Up or Semi-Sub when it comes to moving to a new location, it retrieves it's own anchors and moves to it's next location under it's own steam, just as a traditional ship.

It carries the same drilling crews as a Jack-Up or Semi-Submersible but because it moves around unaided, it carries a larger contingent of traditional marine crew also. Many of the newer built drillships are designed to carry out drilling operations in ultra-deep waters where even most Semi-Submersibles can not drill. These drillships are aided by Dynamic Positioning (DP) systems which use satellites orbiting the earth to fix their position on the sea to within a tiny margin.