On the night of 31 May 1942 three Japanese Type A midget submarines, launched from mother submarines off the Heads, entered Sydney Harbour. Two were destroyed or scuttled inside the harbour and were raised; the third, M24, commanded by Sub-Lieutenant Katsuhisa Ban with Petty Officer Mamoru Ashibe, fired both torpedoes from mid-harbour at about 12.30 am on 1 June. One passed under the Dutch submarine K-IX and struck the converted ferry HMAS Kuttabul, moored at Garden Island as a depot ship, killing 21 sailors.

M24 then slipped back out through the Heads and vanished; for 64 years her fate was one of Australia's enduring naval mysteries. In November 2006 a group of recreational divers from the No Frills Divers club, working the deep grounds off the Northern Beaches, found her upright on sand in 55 m about 5 km off Bungan Head, Newport, just under half-buried. The discovery was announced on 1 December 2006 and a 500 m no-entry Protected Zone was declared the same day under the Historic Shipwrecks Act 1976; the site was added to the NSW State Heritage Register in December 2007 and penalties for disturbance run to A$1.1 million.

The hull is generally intact but damaged by decades of trawling: the conning-tower plating has been torn off and external fittings ripped away. The remains of the two crew are presumed inside, and the site is treated as a war grave, with Japanese family members having visited to lay wreaths. It appears in this file because it is the most historically significant wreck on the Northern Beaches coast and because divers should know that it cannot be dived: access is by heritage permit for research and site management only, notwithstanding a 2012 announcement of occasional controlled recreational dives by ballot.

Technical divers working the Trio, Birchgrove Park and Myola should keep well clear of the zone, which is marked on charts.

Not accessible. The wreck lies about 5 km offshore from Bungan Head between Mona Vale and Newport in 55 m. A no-entry Protected Zone of 500 m radius was declared on 1 December 2006 under the Historic Shipwrecks Act 1976; vessels may not anchor, fish or dive within it, and access is limited to researchers and site managers with permits from NSW Heritage or the Federal environment minister.

Controlled, ballot-allocated recreational dives were announced in 2012 but are not a regular arrangement.

Open ocean 5 km off Newport in 55 m; conditions are those of the Long Reef and Myola offshore grounds – swell under 1.5 m and low surface current needed for any permitted work, best visibility in winter. Irrelevant to recreational divers because entry is prohibited; boats transiting the area should give the charted zone a wide berth in any weather.

No dive plan – entry to the 500 m protected zone is an offence. Permitted survey dives have been conducted by heritage agencies using technical divers and ROVs.

Permit-only. No recreational or technical diving.

No operator – diving prohibited without a heritage permit. Included for completeness of the Northern Beaches wreck record.