Majuro & Mili

The dive plan is written off the tide table, not the clock. Boats leave the town end of the atoll timed to reach the pass at the top of the atoll as the water starts pushing in, so departure shifts through the week and a late tide can mean an afternoon start. The crossing is open lagoon and turns bumpy when the trades are up. When the tide is wrong, the day falls back to sheltered coral heads and island reefs a few minutes from the dock, which is where most second tanks go.

Geographically everything is either outside or inside. The ocean face drops away from a narrow shelf and is dived as a cruise when it is calm enough to sit on. The lagoon interior is a sand basin with coral heads and patch reefs rising off it - shallow, still and forgiving, and the reason a diver who would rather not drift still has a week's worth of diving. The passes join the two: a flooding tide pulls clean ocean water inward, the ride is one-way, and the walls flanking the channel are where the flow concentrates.

Mili is a different proposition - wartime bottom structure rather than reef, lying shallow, with individual airframes identified loosely at best. The atoll held a Japanese airbase that Allied forces bombed and bypassed rather than assaulted, and what is down there is the residue of that. Getting to it is arranged rather than booked: a domestic flight when the schedule holds or a long boat crossing, customary permission from the landowning families, and self-sufficiency once you arrive.

Majuro itself is a working capital rather than a resort island - a strip of road carrying hotels, shops and a commercial port - and travellers who want polish should know that going in. Dive capacity is small and informal, so sites are rarely shared and the operation runs on whoever is available that day. Plans flex too: a bad tide or a blown-out crossing reshuffles the day, so allow more days than you intend to dive.