An ocean bottom seismometer (OBS) recently washed ashore at Wake Island and was shipped to the Hawaii Institute of Geophysics. It appears to be instrument number 4 of the Texas Instrument Mark III series, built in 1964 for the Air Force Technical Applications Center. Some leakage into the sphere is indicated by moderate corrosion of the internal components. About half of the tape was pulled across the head.
Several such instruments were used and lost in experiments (recording of earthquakes and underground explosions) off the Kuril and Aleutian islands in the late 1960s and early 1970s. Some instruments (serial numbers unknown) in the Mark II series may have been lost as early as 1964. Of the 13 Mark III instruments, 11 had been lost as of July 1968; we are unaware of their use (or the use of Mark IV's or V's) in recent years.