Admiralty is the gentle, sheltered option among the Moon Island dives. Grey Nurse Charters describes shallow kelp beds grading into rocky reef with small caves, to about 18 m, sheltered from southerly seas and with historic anchors on the bottom. The north and north-west sides of Moon Island are described in iNaturalist's notes as kelp-covered rocky reefs, in contrast to the walls and caves on the exposed south and east.

The kelp is the first part of the dive. The canopy of Ecklonia sways in any swell, and underneath it red morwong, luderick, mado, silver sweep and wrasse move through the stalks, with cuttlefish, octopus and weedy seadragons possible. Further out the reef becomes more rocky, with ledges and small caves that shelter bullseyes, pomfrets and wobbegongs.

The anchors give the dive a historical thread. The site name hints at the Admiralty-pattern anchors of the nineteenth century, and Swansea's position at the entrance to Lake Macquarie - once a busy coal port with a notoriously dangerous bar - means ships would have anchored off the heads waiting for a tide. Finding the anchors among the kelp and rock is a nice challenge for a guided dive.

With depths mostly under 18 m, plenty of light and shelter from the prevailing southerlies, Admiralty suits Open Water divers, training dives and relaxed second dives. It is less dramatic than The Temple or Under the Tube but reliable when the weather is wrong for the eastern side of the island. It is also a good site for a first night dive at Moon Island, as the kelp comes alive with cuttlefish and octopus after dark.

Boats launch from the public ramps inside Swansea Channel, either at Black Neds Bay beside the Swansea Bridge or at the Swansea/Lake Macquarie ramps, about 25 km south of Newcastle via the Pacific Highway. Parking with trailer bays is available at Black Neds Bay. The run is east along the channel, across the Swansea bar (check the bar and tide first - cross on the flood where possible) and a short distance out to the site; Moon Island sits just off Swansea Heads (Reids Mistake), so the run from the bar is only a few minutes - total 10-15 minutes from the ramp.

Admiralty is on the sheltered side of the island away from southerly seas; the skipper selects the anchoring spot on the day.

Moon Island and the reefs off Swansea Heads sit just outside the Swansea Channel bar, which is the deciding factor on most days: the bar is dangerous in any sizeable easterly or south-easterly swell and on a run-out tide, and Marine Rescue Lake Macquarie should be checked before crossing. Offshore, the sites prefer swell under about 1.5 m and light westerly or northerly winds; a strong nor'easter makes the eastern walls choppy, and a southerly swell pushes surge into the caves. Visibility runs 8-15 m and is best on a flooding tide, when clean ocean water replaces the lake outflow; after heavy rain the brown plume from Lake Macquarie can cover the inshore sites for days.

Admiralty is the Moon Island fallback on southerly days because it is sheltered from southerly seas.

Descend into the shallow kelp, then swim out to the rocky reef and follow it down toward 18 m, checking the small caves and searching for the old anchors. Return through the kelp to the boat.

Grey Nurse Charters (Swansea) runs boat dives to the Moon Island and Swansea offshore sites most weekends and on demand; Dive Newcastle and local clubs also dive the area from private boats launched at Swansea.