On February 12, 2003, the Australian submarine HMAS Dechaineux experienced a critical flooding incident approximately 50 nautical miles off the coast of Perth in the Indian Ocean. A burst flexible hose in the lower motor room allowed seawater to enter the vessel at an estimated rate of one tonne per second, overwhelming the submarine’s ability to surface and placing the lives of all 60 crew members aboard in grave danger.

Commander Peter Scott, in charge of the vessel, ordered emergency procedures aimed at halting the flood and bringing the submarine back to the surface. The crew executed these protocols swiftly and effectively, including blowing the ballast tanks, shutting external hull valves, and increasing speed while angling the submarine at 20 degrees upward—double the standard ascent angle. Despite these efforts, the submarine initially failed to respond, continuing to sink past its maximum designed operating depth.

Aboard the submarine, individuals confronted the likelihood of their deaths in various ways. Petty Officer Geordie Bunting, nearly drowned in the water-filled lower motor room, thought of his wife Arna; sonar operator Melanie Ellerton fixated silently on the depth gauge; while chief engineer John Ryan comforted fellow crew member Michael Morris despite deep uncertainty. The flooded motor room posed additional hazards, as seawater compromised electrical systems, raising the risk of electrocution.

For roughly 20 seconds, the Dechaineux hovered near the ocean floor, with the crew watching the depth gauge anxiously and uncertain if the submarine would survive. Commander Scott later described the experience as deeply harrowing, aware that exceeding the pressure hull’s limits would result in catastrophic failure. In reflections published in his 2023 memoir, Scott recounted moments when thoughts of his family competed with his responsibility to lead and maintain composure amid crisis.

Eventually, the flooding halted after valve closures, and the submarine ceased sinking. Slowly at first, it began to regain depth and finally surfaced, breaking through the Indian Ocean’s surface after what was described as an intense and silent ordeal. However, the ordeal was not over. Damage to critical systems, including the main motor cooling gear, left the Dechaineux operating with severe speed restrictions, and the threat of further flooding remained as the submarine embarked on the slow journey back to HMAS Stirling naval base in Fremantle.

The incident raised significant questions about the safety and resilience of the Collins-class submarines to which the Dechaineux belongs. Naval officials faced the challenge of managing the technical and operational consequences while addressing the psychological toll on the crew. Although the submarine ultimately returned safely, discussions around transparency and the handling of such near-disasters persisted within naval and public spheres.

The event remains a poignant example of the dangers faced by submariners and the critical importance of training, discipline, and quick decision-making during life-threatening emergencies at sea.