HMAS Warrnambool was a Bathurst-class corvette, 57 m long, that served through World War II and earned battle honours for Darwin 1942, the Pacific 1942–45 and New Guinea 1942. After the war she was engaged in clearing the mines laid across the approaches to northern Australia. On 13 September 1947, while sweeping near Cockburn Reef off northern Queensland, she struck a mine and sank, according to Wikipedia; four sailors were killed and 29 injured.

She remains the only Royal Australian Navy ship sunk by a mine. The wreck lies in about 25 m of water. Marine Life Network's Torres Strait page describes it resting on its port side with military artefacts in place, calling it one of the few intact warship wrecks in Australian waters.

A 2016 Royal Australian Navy hydrographic survey by HMAS Mermaid, reported by Maritime Executive, found the wreck remarkably well preserved after 69 years and home to marine life. The wreck was sold to a salvage company in 1972, but the survey shows it remains largely intact. There is no regular dive operator.

The site is remote – off the northern tip of Cape York – and is not on the scheduled far-northern liveaboard itineraries. Anyone contemplating a dive would need a private expedition, and should check its heritage status: as a naval vessel sunk more than 75 years ago, it is covered by the Underwater Cultural Heritage Act 2018, which protects wrecks over 75 years old; a permit is needed to disturb it, and navy war graves considerations apply given the loss of life. The possibility of unexploded ordnance from the minesweeping operation and the ship's own armament cannot be ruled out.

For wreck enthusiasts, Warrnambool is an intact WWII-era warship in clear tropical water – but one of the hardest wrecks in Australia to reach.

Liveaboard only – there are no day boats, resorts or public moorings this far north. Mike Ball Dive Expeditions' Spoilsport runs 7-night 'Northern Exposure' expeditions between Cairns (Trinity Wharf) and Horn Island in the Torres Strait each November (northbound and southbound, up to 27 dives), plus a 7-night Far North Coral Sea Exploratory round trip from Cairns in October. Spirit of Freedom runs 7-night far-north expeditions from Cairns in October–December, and Professional Dive Services' MV Kalinda has run longer (13-night) Cairns–Horn Island trips.

Horn Island has daily scheduled flights to Cairns (book separately; allow 24 hours after diving before flying). The far-northern reefs are roughly 500–650 km north of Cairns – one to two days' steaming each way.

The far-northern reefs are only diveable in a narrow weather window. The south-east trades blow hard from about April to September and make the long open-water passage and the exposed outer walls impractical, so expeditions run in the transition period, typically October–December, when winds are lighter; the northerly monsoon, storms and cyclones (December–April) close the season. Even in the window, exposed shelf-edge walls (Tijou, Great Detached, Raine) need calm days, and skippers switch between reefs to find shelter.

Strong tidal currents and upwellings run along the continental shelf and through reef openings – channel sites are timed to slack water. Visibility varies from about 12 m to 40 m+ depending on tides and any rain. Marine stingers are present from November.

If dived on an expedition, descend a shot to the hull (lying on its port side in about 25 m), tour the exterior from bow to stern without entering, noting the military fittings in place, and ascend the line for a safety stop. Treat any ordnance as live.

25 m depth: nitrox EANx32 extends NDL; no penetration without wreck training and permission; heritage-protected (UCH Act 2018).

No regular operator – not on scheduled liveaboard itineraries; visited only by rare private or survey expeditions.