I-124 was one of four large minelaying submarines built for the Imperial Japanese Navy in the late 1920s, based on the German Type UB III design obtained after World War I. In January 1942, as Japanese forces pushed south, she laid mines off Darwin and waited to attack Allied shipping. On 20 January 1942 she was detected and sunk off Darwin by the corvette HMAS Deloraine, supported by other Australian warships, US destroyers and aircraft, using depth charges and bombs. About 80 crew went down with her. She was the first enemy submarine sunk by the Royal Australian Navy and the first full-size submarine sunk in Australian waters.

The wreck lies in about 45 m roughly 50 nautical miles north-west of Darwin. In 1972 salvagers located her, hoping to recover scrap metal and supposedly valuable cargo; Japan objected to disturbance of the war grave, and in 1977 a salvager detonated explosives at the site, severely damaging the conning tower, in an attempt to force negotiations. The Navy secured the site, and it became Australia's first protected war grave. A Flinders University and NT Heritage survey released a virtual-reality model in 2022 showing the hull still mostly intact, with some degradation of the outer hull.

The site is a declared protected zone with a closed-water order and entry requires Heritage Branch permission. Given its depth, it would in any case be a technical decompression dive. It is included here because it is often asked about and to make clear that it is not open to recreational divers; the VR model is the way most people can see it.

The wreck lies about 50 nautical miles north-west of Darwin in open water in the approaches to the harbour. It is a declared protected zone with a closed-water order and is treated as a war grave: vessels may not enter the zone and divers may not visit without permission from the NT Heritage Branch, which is granted only for approved research and management. There is no recreational access.

Open water in Beagle Gulf, fully exposed; research visits are made in the dry season (May–October) on calm neap-tide days. At 45 m in the approaches to Darwin the tidal stream runs strongly for most of the cycle, so even permitted teams work only short slack windows on neap tides. The wet season (December–April) brings monsoon north-westerlies, storms, cyclone risk and box jellyfish.

The site is closed to recreational divers regardless of conditions.

Not applicable – closed site.

If ever accessed under permit: trimix/decompression dive at 45 m in open water with strong tidal streams.

None – closed-water protected zone and war grave; access restricted to permitted research teams.