Rabaul, East New Britain, PNG tide times

Rabaul sits inside Simpson Harbour, a near-perfect circular bay at the northeastern tip of New Britain Island: the drowned remnant of a volcanic caldera roughly 8 km across, its crater walls forming the rim of hills that surround the harbour on three sides. The single navigable entrance through Blanche Bay to the northeast made this harbour coveted by every colonial and military power that understood Pacific geography. The German colonial administration chose Rabaul as the capital of German New Guinea precisely because of this harbour. The Imperial Japanese Navy chose it as the hub of its South Pacific operations for the same reason.

From January 1942 to August 1945, Rabaul was the most heavily fortified Japanese base in the South Pacific. Over 100,000 Japanese troops were ultimately garrisoned here; the tunnel networks hand-excavated into the volcanic hillsides ran for hundreds of kilometres, accommodating submarine pens, hospital wards, ammunition stores, command centres, and aircraft hangars. After Allied air superiority cut the sea supply lines in 1944, those 100,000 troops remained in place — cut off, slowly starving, but never defeated in the field. They surrendered in September 1945 after the war ended. The tunnels are the most extensive surviving example of Japanese WWII fortification in the Pacific; guided tours run through the accessible sections, including the submarine pen and the Japanese barge tunnels at Tavurvur's base.

Then on 19 September 1994, Tavurvur volcano on the eastern harbour rim and Vulcan on the western rim erupted simultaneously. Pyroclastic flows and ash falls buried most of the Rabaul town centre in 24 hours. The 1994 eruption produced one of the most-filmed volcanic events in Pacific history; the photograph of ash-buried Rabaul church towers became the iconic image. The new administrative and commercial centre relocated to Kokopo, 20 km east. Old Rabaul is not demolished — it is partly preserved under and around the ash: the pre-eruption street grid visible in places, some buildings partially excavated and re-used, the intact colonial-era Chinese shophouses standing on the waterfront strip.

Tavurvur still vents steam daily and has erupted on a smaller scale since 1994. The Rabaul Volcanological Observatory monitors activity continuously and posts access advisories; the viewpoint on the caldera rim road gives a direct line of sight to the active crater and is typically open. Climbing the cone requires checking the current advisory. Pacific semidiurnal, spring range 1.5 to 2.0 m at Simpson Harbour. The caldera geometry produces a modest tidal current at the single harbour entrance; the WWII wreck sites inside the harbour are accessible at all tide states, though the entrance current of 0.5 to 1.5 knots on the ebb is relevant for dive boats timing their passage out to the deeper sites beyond Blanche Bay. Predictions on this page come from Open-Meteo Marine (gridded model, ±45 min / ±0.2–0.3 m). The Gazelle Peninsula cultural landscape around Rabaul includes the Tolai people's traditional baining ceremony practices — fire dances using large baining masks conducted at initiation events — which are occasionally accessible to outside visitors through cultural tour operators in Kokopo. The Kokopo Cultural Centre in the new town holds artefacts from the colonial, WWII, and traditional Tolai periods in a well-organised museum format; the WWII section complements the outdoor tunnel and field site visits. The Rabaul Caldera is an active volcanic system, and the volcanic cones of Tavurvur and Vulcan sit at the caldera rim close to the water. Tavurvur erupted most recently in 2014, covering much of the former town in ash. The area's extraordinary geological history attracts a specific category of traveller willing to navigate the limited infrastructure; understanding tidal state is essential for accessing the ash-covered foreshore and for timing boat trips to the Simpson Harbour islands. The Simpson Harbour anchorage inside the caldera is one of the most dramatic in the Pacific; yachts shelter here during cyclone season (November through April) but tidal range, at around 1.3 m, is manageable for most deep-keeled vessels. Fishing from the volcanic rock platforms on the caldera rim is influenced by tidal state; the platforms are exposed only at low water and require careful footing on the rough lava surface. War history diving — the harbour holds numerous Second World War wrecks including Japanese Zero fighters and midget submarines — is largely tide-neutral given the depths involved, though surface conditions at the caldera entrance improve on the slack.