1. In a drill string exposed to natural environmental conditions in reach from an immersed drilling station established on the floor of a body of water to an immersed buoyant support means above from which the string suspends and said string retained as an integral assembled length established when said support means is in vicinity of the water surface with the drill bit below said station, the improvement comprising: a. a coupling having mating halves and connecting adjacent ends of a multiplicity of rigid tubular members with equal space sequence measurably less than the length of the torque imparting tube of the drilling station that accommodates uninterrupted passage of the string through the tube with descent of the support means to the station; b. torque transfer means formed to the couplings continuously transmitting power from the drilling station to thE drill string depending depending upon successive couplings to become in torque transfer engagement with said tube prior to exit from the tube of an adjacent coupling; c. a spline type engagement of the mating coupling halves formed to the ends of each tubular member providing unselected assembly of members to procure integrity of longitudinal alignment of all said torque transfer means of the integral string length; d. snap type ring means locking the said halves together for the couplings to transmit as tension to the connected upper member the weight of the string portion below the coupling; and, e. sealing means protecting coupling inner parts and sustaining fluid flow between connected rigid members.