Guam

Guam dives like a place with roads. Shops collect divers from the Tumon hotel strip, and a good part of the week can be shore entries, walking in off a beach with the tanks left in the truck. Boat trips run out of Apra Harbor and are short. The harbour sites sit inside an active naval port, so access is arranged in advance through a local shop and can be restricted at short notice when port operations require it, which is worth knowing before building a whole trip around the wrecks.

Northern Guam is an uplifted limestone plateau and the reef follows suit: a shallow shelf punched with sinkholes and cavern mouths, then an abrupt edge where it drops into open water. Off the Orote Peninsula on the west side the wall is the main event, dived as a run along the face. Inside the harbour it is the reverse, flat and silty and darker, with visibility that depends on rain and port traffic. The two feel like different destinations reached from the same pickup point.

War material is scattered well beyond the named wrecks. Landing craft, amphibious tractors and unidentified debris lie in the shallows off the July 1944 invasion beaches at Asan and Agat, much of it within the War in the Pacific national park, where the relics are protected and nothing should be lifted. Identifications on the smaller pieces are often uncertain, so treat confident labels with some caution. The big harbour wrecks are silty and deep enough to make for short dives, and are best planned without penetration unless you carry the training.

Timing decides how much of the island you actually get. December to May is the settled stretch, when the outer wall and the northern reefs are reliably in reach, and June usually still works. From July to October the typhoon season puts the exposed sites on and off, diving retreats into the harbour and the lee, and a trip then needs spare days; November is the turn back. It also works unusually well as a short stop, since a full day underwater is possible without boarding a boat.