The Song Saigon is the largest of Darwin's Vietnamese refugee boats and the centrepiece of the harbour's artificial-reef complex. Unlike the wooden fishing boats in which most refugees arrived, she was a steel vessel of about 40 m (130 ft) and 200 gross tons, described variously as a small tanker or coastal trader. DSAC records that she was hijacked and sailed to Australia by refugees; she brought 34 people to Darwin in 1979. Between 1976 and 1981 more than 50 boats carrying Vietnamese refugees reached Australia's northern coast, most of them arriving in Darwin Harbour. Several of the steel boats were later cleaned and scuttled west of Cullen Bay together with a redundant construction barge to create a fishing and diving reef, and the site was extended in later years with a confiscated illegal fishing boat. The group sits in 20-25 m within a few hundred metres, and some operators have linked the wrecks with rope so that more than one can be visited on a dive. The Song Saigon was scuttled in 1982 by the Dinah Beach Cruising Yacht Association, the Darwin Amateur Fishing Association and the NT Fisheries Division.

She sits upright and relatively intact on the bottom in 21-25 m. Several of her holds and the deckhouse are open and can be looked into with a torch, and after four decades the hull carries good coral and sponge growth. Fish life is very good: golden snapper, cod, jewfish, batfish and trevally swarm the structure, and stonefish sit camouflaged on the deck and superstructure. Being the most ship-like of the complex, it is usually the first wreck divers visit here, and with the John Holland Barge and the Ham Luong so close it is one of the few places in Darwin where you can see several wrecks in a single neap-tide window. Local divers suggest taking several slow dives rather than trying to rush all three.

Boat only. The refugee-boat complex lies in the outer harbour a short run west of Cullen Bay - typically 10-15 minutes from Cullen Bay Marina or the Cullen Bay public ramp (off Marina Boulevard, trailer parking on site). NT Fisheries publishes the positions of each wreck for anglers, so expect fishing boats on the marks on neap weekends.

Drop a shot beside, not into, the structure, and plan to be on site before high-water slack; the complex is exposed to the full tidal flow once the tide turns.

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.

Descend the shot to the deck at about 20 m, tour the upright hull from bow to stern, look into the open holds and deckhouse with a torch without entering, then follow the connecting line (if in place) towards the Ham Luong or John Holland Barge. Turn with enough gas to return to the shot for the ascent.

Darwin Dive Centre and Dive Darwin include the Vietnamese refugee boats and artificial-reef wrecks in their neap-tide harbour charters; Darwin Sub Aqua Club dives them regularly on club days. No fixed daily schedule - trips follow the neap cycle.