IJN Iro (Palau — 120 fsw)


The Imperial Japanese Navy (IJN) Iro was an oil tanker built in the early 1920s in Osaka, Japan. It is a relatively large wreck with a length of 470 feet and a beam of 58 feet. Unlike some of the other wrecks in Palau, the Iro was NOT a merchant ship that was converted for wartime use. It was commissioned and built specifically as a Navy oil tanker.

Iro in wartime camouflage scheme (from Combined Fleet website)

The Iro was powered by a triple-expansion engine and had a cruising speed of 9 knots and a maximum speed of 14 knots and had a crew of 160. She was fitted with two low-angle 5.5-inch, 50 caliber guns on rotating platforms — one at the stern and one at the bow. She also had two high-angle anti-aircraft guns and four machine guns.

The Iro has a lot of interesting backstory and she was an active oil tanker throughout the Pacific in WW II.

A week before Operation Desecrate 1, she was part of a large convoy that was spotted by the US submarine USS Tunny. A battle ensued between the US submarine and the Japanese escort destroyer Michishio. During that battle, the Iro was hit by a torpedo in the bow, ahead of the collision bulkheads.

The Iro was badly damaged but didn’t sink and limped off to Palau for repair on 23 March 1944.

Seven days later Operation Desecrate 1 began. Tankers were valued targets and the Iro was quickly spotted by the dive-bombers which dropped six 1,000 pound bombs in her vicinity and reported one hit. However, she was still afloat a day later when a squadron of SBD Dauntless bombers attacker her again. She was hit by another 1,000 pound bomb on the starboard aft quarter. The bomb had a delayed fuse and exploded right in the engine room which resulted in a large fire.

Due to the various watertight compartments in her design, she was mortally wounded but didn’t sink right away. The stern started to sink and the bow strained the anchor and titled up into the air exposing the earlier torpedo damage. Rod Macdonald has some great pictures from the National Archives of the Iro half sunk with the bow sticking up. She continued to burn for several days and then sank almost three weeks later on 17 April 1944.

The Wreck

The Iro sits upright in about 120 feet of water. Given the size of the ship, it is hard to see all of this wreck on one (or even two dives). I got two dives on the Iro and could easily spend more time on it (and plan to when I return).

Below are diagrams from Rod’s book and from Fish ‘N Fins / Oceanhunter which give a good overview of the wreck (note that Rod’s diagram looks more “correct” to me).

Some of the highlights of this wreck include:

  • Torpedo damage from the USS Tunny is obvious at the bow of the wreck
  • The engine room is massive and easily found/visited
  • There are still barrels with oil in the holds
  • The gun at the stern is on a massive turret which makes for a good wide angle picture from above
  • The masts and king posts are encrusted with coral and sea life. Really amazing sights.


Below are some of the photos I took during the two dives.

Bow Section

The bow section makes for a good wide angle natural light photo if you get good visibility. We had pretty good conditions but there was some particulate matter in the water. Here are some photos from the second dive.

Amidships area

Below are photos swimming into and through the bridge superstructure (which is forward of amidships) at the deck level towards the stern.

Massive twin goalpost masts aft of the bridge superstructure
Port side davit swung out to see indicating that the lifeboats had been used

Deckhouse area pictures:

Engine Room

The engine room is relatively open with gratings and catwalks everywhere that are jumbled up and distorted from the bomb explosions that pierced the outer shell of the ship and exploded inside the engine room area.

Stern Area

Below is a large 30 foot tall refueling tripod that was used to facilitate Replenishment at Sea (RAS) operations.

Below are some photos of the large 5.5-inch gun mounted on the circular platform at the stern on top of the poop.

As mentioned above, the masts of the Iro have an amazing amount of sea life on them and some beautiful coral. I could spend a whole dive just looking at the masts. Below are a few pictures I snapped while ascending and completing my safe stop.


Combined Fleet movement record

Dive Palau The Shipwrecks by Rod Macdonald

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