The NR Diemen is widely regarded as one of the most intact wrecks in Darwin Harbour and one of the easiest to enjoy. She was a 73 ft (about 20.5 m), 124-ton steel research trawler that broke from her moorings at Stokes Hill Wharf during Cyclone Tracy and drifted across the harbour before sinking near Mandorah. Cyclone Tracy crossed Darwin in the early hours of 25 December 1974 with gusts estimated at over 200 km/h, destroying most of the city and killing 66 people, many of them at sea.

More than 20 vessels sank or were driven ashore in and around the harbour, and several of those wrecks now form a second, much more intact wreck trail beside the 1942 sites. She sits upright on a sloping sand bottom with her bow rammed into the shore facing west and her stern facing east in about 12 m. The top of the trawling gantry comes to within a metre or so of the surface at low tide and can be seen from a boat.

Because of her east-west orientation the hull offers shelter from the tidal stream, and the wreck stays relatively clear of silt compared with the harbour's other sites. Fish life is some of the best in the harbour: black jewfish, groper, barracuda, trevally, mackerel, tuna and rock cod patrol the structure, and wobbegongs rest on the deck. With a maximum of 12 m, a recognisable ship shape and the chance of good fish encounters, the Diemen is the standard first wreck for newly certified divers in Darwin and a good training site, and it is also rewarding for photographers on the rare days of better visibility.

The shallow gantry also gives snorkellers something to see on a clear neap.

Boat only. Launch at Cullen Bay Marina or the Cullen Bay public ramp and cross the harbour west towards Mandorah on the Cox Peninsula, a run of around 15-20 minutes in calm conditions - the SeaLink ferry route from Cullen Bay to Mandorah jetty gives the line. Watch for the ferry on approach.

Mandorah can also be reached by road (about 130 km around via the Cox Peninsula Road), but the site itself still needs a boat. Plan to arrive for the neap high-water slack.

Tide is everything in Darwin Harbour: the spring range is 7-8 m and tidal streams run hard through the harbour, so diving is generally only possible on neap tides (range under about 3-4 m), timed to the slack at high water when clearer ocean water sits over the site. Spring tides bring strong currents and silt-laden water with near-zero visibility. The dry season (May-October) gives the most consistent conditions; the south-east trade winds can chop up exposed water in the afternoon, so mornings are best.

In the wet season (November-April) run-off from the rivers and creeks drops visibility, afternoon storms build quickly, and the harbour is in cyclone season; box jellyfish are present October-May.

Anchor off on the sand, not on the wreck. Descend to the stern in 12 m, swim forward along the upright hull past the wheelhouse to the bow pushed into the sandy slope, then return on the other side, finishing in the shallows around the trawling gantry. The east-west lie gives a lee from the tide on one side.

Darwin Dive Centre and Dive Darwin run harbour wreck charters only on neap-tide windows (typically a few days either side of each neap, weekends favoured); Darwin Sub Aqua Club dives it on club neap-tide days (members plan dives at Thursday meetings at the Darwin Ski Club). No daily schedule.