During her military career, Protector supported the trials of the Collins-class submarines, and was involved in a search for the shipwreck of the World War II cruiser HMAS Sydney.

The ship was decommissioned in 1998 and, while still owned by the Commonwealth, she is provided to Defence Maritime Services to allow them to support Navy activities under contract.

Renamed Seahorse Horizon, the ship is operated by Defence Maritime Services out of HMAS Creswell as a training and Fleet support vessel.

The ship was purchased by the RAN on 18 October 1990, fitted with a LIPS dynamic positioning system, two Remotely Operated Vehicles and a recompression chamber.

On 10 June 1995, Protector was slightly damaged when a switchboard malfunction aboard HMAS Collins caused the submarine to ram the trials ship.