Roach Island is described by Diveplanit as the largest of the group of seven Admiralty Islets – other sources give that title to Sugarloaf, so treat the claim with care – and it is the anchor point for several of the northern dives. Diveplanit's survey covers the Admiralty sites together, with a top around 18 m, a median depth of 22 m and a bottom around 30 m. It describes steep drop-offs presented as walls of coral, bommies and large boulders, and swim-throughs where the islands meet below the surface. Flat Rock, a low rock beside Roach Island, is dived as part of the same complex.

The reef here is typical of the Admiralty Islets: hard coral and gorgonian fans on the rock, boulders and gutters on the slopes, and sand at the base. Diveplanit's divers recorded tasselled flathead, mosaic moray, black-and-white lionfish including juveniles, dusky hydroids, gorgonian fans, blue nudibranchs and painted morwong, plus an unusual bannerfish-like species. Galapagos sharks are the most common large animal, and kingfish, trevally and drummer school along the edges. Occasional mega fauna – turtles, rays and passing pelagics – turn up as well.

Because there are several faces to choose from, operators use Roach Island in a range of conditions, diving the side sheltered from the day's wind. The swim-throughs are a highlight and are generally wide and short, but they surge in north-east swell. Roach Wall, dived by Nigel Marsh, is the island's steeper face and is listed as its own site here.

The dive suits Open Water divers in calm conditions, with Advanced certification preferred because the walls pass 20 m. It is a scenic dive with both macro and occasional big-animal interest.

Lord Howe is reached only by air: QantasLink flies from Sydney daily (about 1 h 50 min), with Brisbane and seasonal Port Macquarie services. Accommodation must be booked before flights (visitor numbers are capped at about 400) and the checked-baggage limit is 14 kg, so most divers hire gear on the island. Dive Lord Howe's shop is at 2 Lagoon Road beside the Lagoon Beach boatsheds; most lodges transfer divers or it is a short bike ride.

Divers board the boat, which is moored in the lagoon, and exit the lagoon through North Passage, then run north-east around North Head to the Admiralty Islets, a group of seven rocky islets a few hundred metres to about 1.5 km off the island's north-east tip. The trip takes about 20 minutes. The boat anchors on sand or a small reef close to the site or runs live if there is current.

Lord Howe sits in the path of the prevailing south-east to east trades and winter westerly fronts. The Admiralty Islets are exposed to north-east and easterly swell and to northerly winds, which blow them out; they come into their own in south-westerly to southerly winds, when the island shelters them and the southern and western sites are rough. A 1.5 m swell from the north-east makes the shallower gutters surgy, and a lump above about 2 m stops the trip.

The Coral Sea current washes these islets more than other sites, so currents can pick up, especially on the outer edges. Visibility is typically 30–40 m. Best months are February–May; winter westerlies are fine here if the swell is down.

Anchor in the lee of Roach Island. Descend to 18–22 m and follow the coral-covered drop-off along the island, detouring through swim-throughs where the islets meet below the surface. Watch the blue for Galapagos sharks and the boulders for morays and lionfish.

Turn at half air and return shallower to finish on the boulders near the anchor.

Dive Lord Howe (PADI 5-star, 2 Lagoon Road) – morning double boat dives daily in season, afternoon single dives on demand; site chosen on the day by wind and swell. Howea Divers has also advertised dives here.