The British Motorist was a 6,891-ton steel tanker built in 1924 by Swan, Hunter and Wigham Richardson in Newcastle upon Tyne for the British Tanker Company - a 134 m, single-funnel motor ship with an eight-cylinder oil engine good for 11 knots. On the morning of 19 February 1942 she was in port refuelling the destroyer USS Peary when the raid began. Two bombs hit her: one destroyed the bridge and a second struck forward.

She listed to port, caught fire amidships and capsized, sinking on her side. Her master, Captain Gilbert Bates, and the second radio officer were killed out of a crew of 61. For years half of the hull was exposed at low water.

The 19 February 1942 raids - two waves of Japanese carrier and land-based aircraft, the first and heaviest attack ever made on mainland Australia - sank eight ships in the harbour and killed more than 230 people. In 1959-60 the Japanese firm Fujita Salvage cut most of the wrecks down to or below the waterline for scrap, so what divers find today is usually the lower hull, machinery that was too heavy to lift, and the cargo that the salvors were not permitted to remove. The British Motorist was the first ship Fujita raised.

The salvors cut her into sections, welded the fore and aft parts together and towed them to Japan for breaking, and in the meantime she served as storage and living quarters for the Japanese salvage crews working the other wrecks. The engine room was too heavy to lift and was left behind, so today's dive is a compact block of machinery and a jumble of artefacts spread over a silty bottom in 18-20 m. It is the least visited of the big raid wrecks because there is less structure to follow, but it is close to the wharf, easy to reach, and holds good numbers of snapper and rock cod around the machinery.

It suits divers who have already done the Meigs and Zealandia and want to complete the set of 1942 sites.

Boat only. Darwin's charter operators leave from Cullen Bay Marina or the Darwin Waterfront precinct and run across the harbour to the site in well under half an hour on a calm neap-tide morning. Private boats can launch at the Cullen Bay public ramp (west of the CBD off Marina Boulevard), the Stokes Hill / Frances Bay ramp beside the Waterfront, or the East Arm ramp for the southern anchorage.

Mark the position on GPS before the dive - the wrecks lie in open water with no surface marker - and drop a shot rather than anchoring into protected structure. Parking and trailer bays are at all three ramps; air fills and hire through the Darwin dive shops.

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.

Drop the shot on the engine-room remains at neap slack, circle the machinery block first, then make short excursions out into the surrounding debris, always keeping the main structure in sight in the poor visibility. Hold 16-20 m, return to the shot and ascend with an SMB.

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.