Method and apparatus for emplacing a structure such as a casing, piling or core barrel into the floor of a body of water, hereafter referred to as sea floor. The structure is mounted on a towable and submersible vessel which includes a number of ballast tanks, and means are provided to selectively vary the ballast in certain ones of the tanks in a manner causing the vessel to have selectively controllable negative or positive buoyancy for descent or ascent, respectively, to or from the sea floor. A support device on the vessel is adapted to move the structure between a horizontal orientation for towing and descent and an upright position for drilling. after the vessel reaches the sea floor. The vessel descends with a positive metacenter to maintain the established orientation until it reaches the sea floor, after which it is anchored and leveled for commencing the drilling operation. The structure is advanced into the floor through increments of drilling strokes by means of rotating, through oscillatory or continuous rotary motion, a clamping mechanism which is engaged at incremental positions along the length of the structure. Means are provided to control the thrust force between the drilling end of the structure and the sea floor. An umbilical cable supplies power and control functions from a surface ship to the submerged vessel. Water under pressure is circulated through the interior volume of the structure to carry cuttings material away from the cutting end. Following completion of the drilling operation grout material is pumped into the void spaces between the structure and sea floor. The vessel is recovered for subsequent use by disengaging the clamping mechanism from the structure and blowing selective ones of the ballast tanks to cause the vessel to have positive buoyancy.