The drilling vessel GLOMAR CHALLENGER has the requirement of maintaining a relatively fixed position in the deep ocean for periods as long as two weeks. The vessel's position is maintained by a dynamic positioning system that uses a sea‐floor acoustic beacon for the position reference. This beacon, which is free falling and nonrecoverable, provides an acoustic signal consisting of a 4‐msec pulse of energy at a frequency of 16 kHz every 2 sec; the beacon is battery operated and can be used in water depths up to 20 000 ft. This acoustic reference system has been used in drilling operations for over 2 yr with very satisfactory performance.