A new acoustic tracking system recently completed a week-long sea trial with a tethered submersible vehicle. The vehicle made increasingly deeper dives, reaching a maximum of 500 ft, while the SS400TS Acoustic Tracking System tracked its position relative to the operating ship. In an unscheduled test the tracking system also monitored the location of a wellhead inadvertently dropped to the muddy bottom before its position could be buoy marked. The submersible was successfully navigated to the transponder on the wellhead with the range and bearing information from the SS400TS. The tracking system is manufactured by Western Marine Electronics of Seattle.