Olympia Maru

From the main deck, at 18 to 24 metres, the hull lies level beneath you and the cargo holds open to daylight. She sits upright and the currents are generally calm1, so the layout is easy to hold in your head.

The port side is where the colour is. Black coral grows in bright orange bushes over the hull and along the flank, and the anemones there shelter clownfish1. Big puffers cruise past with remoras on them and scorpionfish sit along the rails2, while giant batfish gather around the mast, bow and stern.

Inside, one route goes from the rear hold through a small gap into the second hold, past what looks like a prison cell, into the engine room beside the boilers with their exposed tubes, and out through tight swim-throughs in a deckhouse2. The other enters at the stern through the sterncastle and finds coils of line, a stash of bottles, a large boiler and crushed fuel drums, then cargo holds with blue light streaming in3.

She burned before she went down, so the upper deck is deformed and the masts no longer stand straight1.

In October 1941 the Imperial Japanese Army finished converting her into an auxiliary aeronautical repair ship, and its 18th Shipping Air Depot was organised and carried aboard her4. She began as a cargo ship, but the ship that sank at Coron was a floating workshop for aircraft with its unit on board.

The dive suits different divers in different ways. Calm water and daylight in the holds make the main deck a relaxed dive for an Advanced Open Water diver, while the deeper water below it and the overhead spaces inside are for the wreck trained.

At night the same hull is reported to be quieter, with sleeping fish and turtles tucked into the structure2.

She was built at Nagasaki as a 5,612-ton cargo ship and converted from steam to diesel in the summer of 1930. Her launch date is disputed, with 1927 and 1920 both on record4.

The Army requisitioned her on 21 July 1941. Conversion began at Shimonoseki on 3 September and finished on 25 October4. In September 1944 she reached Coron Bay and anchored just west of Tangat Island on the 23rd, reportedly laden with rice and supplies for the occupation forces. On the 24th American carrier aircraft attacked the anchorage. About 40 dive bombers are reported to have come in around nine in the morning while she was under way and trying to evade, and fire spread across the ship and bent her midship section. She sank by the stern4.

For years divers knew her only as the Tangat wreck, after the island beside her, until she was identified2, and the wreck now called the Morazan had been taken for her3.

Coron divers warn that guides sometimes lead people with little wreck experience far inside, and an operator describes easy penetration at the cargo rooms of this one. Operators list a Wreck Diver specialty for going in. Ask to be shown the entrance and the plan before you agree, carry a torch, and keep the exit in view.

Scorpionfish and crocodilefish sit on the wreck and hydroids grow in the coral cover on the flank, so hover and keep your gear tucked in.

Settle your working depth before you descend. The main deck is a long, relaxed dive, and the sand near 30 metres is a different one. A night dive adds darkness to an overhead environment, and it stays outside the hull unless everyone is wreck trained.

Where the fire passed, the structure is not sound. A visiting diver was warned that some decks were starting to pancake on top of one another3, so keep out of the buckled sections.