A piece of Australia's military history is facing a watery demise at the bottom of Darwin Harbour after it sank last week.

The HDML 1321 was a boat used by Australia's elite Z Special Unit[1] during World War II.

The Z Special Unit was an elite commando force established by the Australian Army during World War Two and is seen as the foundation of the modern SAS.

Soldiers relied on specially designed vessels like the HDML 1321 to allow them to undertake covert operations in the Pacific.

In 1945, eight commandos used the vessel to go behind enemy lines in Papua New Guinea as part of Operation Copper [2] [3].