The greatest concentration of World War II shipwrecks on the planet lies in a remote lagoon in the middle of the Pacific Ocean. Today the island of Chuuk is a backwater, but in 1944 it was the centre of Japanese naval operations in the Pacific, until Operation Hailstone, an airstrike which was the US payback for the attack on Pearl Harbour. Over two days, American planes sunk around 40 Japanese ships at their anchorages. Most of the ships lie on the sea floor still intact. Many still contain cargoes of planes, tanks, weapons and munitions. Ghostly corridors lead to engine rooms, cabins, and long abandoned bridges with controls still intact. Bones and skulls are still commonplace.