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Truk Lagoon's Top 5 Most Challenging Dives - Part II

March 30, 2021  •  Leave a Comment

Truk Lagoon's Top 5

Challenging Dives - Part II

Photos & Text by

Mike Gerken

Read "Part I": "Truk's Lagoon's Top 5 Most Challenging Dives"


Diving the wrecks of Truk Lagoon over the past 20 years has produced many memorable experiences but none as challenging as the top 5 listed in this article. Below are my accounts of the top two. My friends and dive team members, Keisuke Yokota and Eri Umino concur with the ratings in this list. For background and the other top 3 wrecks please see the link above.


#2 The Amagisan Maru

The TelegraphThe telegraph is a key reference for navigating around the lower engine room.             If there is a single dive etched into my memory it was a hair-raising one several years ago on a foray into the heart of the Amagisan Maru. The Amagisan was torpedoed and sank in 190’/58m with the top of the wreckage at 110’/33m. This wreck appeals to divers with a wide range of skills from advanced to expert. However, the lower engine room of this 450’ merchant ship is complex and not for everyone. The ship lays 75 degrees on its port side making it extremely disorienting 3 levels down inside the wreck at 180’/55m. To make matters worse, the visibility is often poor and the stairwells are blocked by debris. The Amagisan Maru Torpedo striking the Amagisan Maru.

            Entering the lower engine room is easy but, like a maze carved out of hedges, exiting is the hard part. On my first “memorable” exploratory dive I become momentarily lost in the hazy water. Losing your bearings even for a mere few minutes at that depth seems like an eternity. Without citing the half-dozen rules I violated let me just say it was complacency that nearly caused my demise. After this humbling experience, I went back to the Amagisan engine room a week later with a proper plan and imprinted the route to memory. It took 3-4 progressive dives to learn this section of the wreck but when I was done it became as familiar to me as my own bedroom.

            Phone BoothOnly remnants of the wooden phone booth remain with the handset at the end of the white cord. There are some interesting attractions inside the engine room and knowing there are very few who have seen them makes the dive more exciting. The telegraph and master controls are within a few feet of each other and are an important reference for navigation. Moving away from the control room there is a decayed wooden phone booth (right photo) with handset, cable and ringer still intact. Of course, the usual racks of gauges, valves, whatchamacallits and thingamabobs are plentiful and cool to look at. Diesel powered cargo vessels were modern technology in the 1930's and 1940's while today it looks archaic. This engine room is one of the largest I have explored and have yet to see it all.


The TelegraphKeisuke examines the telegraph in the hazy engine room.

The ExitKeisuke exits the engine room through the skylight.

Engine RoomThe Upper Engine Room



#1 Aikoku Maru 

Aikoku MaruAikoku MaruJapanese merchant raider, Aikoku Maru in WWII.

The Control RoomKeisuke and Umi explore the control room in the heart of the Amagisan Maru.
            Thump, thump, thump. “What was that sound?”, I thought to myself while penetrating deep into the engine room of the Aikoku Maru. It became clear after a moment that is was the din of my pounding heart. No other dive in Truk Lagoon has made me feel such a way. Maybe it is the deep depth or the complex penetration or maybe it is the souls of the dead that haunt me.

            This 500’ long merchant raider met a fiery end when the entire forward half of the vessel erupted in a massive explosion during "Operation Hailstone". The blast killed over 700 men and annihilated half of the ship. The upper engine room collapsed but the lower section is partially intact. Navigating to it at over 180’/55m is no easy task.

  Fuel Site GlassesWhat is believed to be sites for examining the fuel.            Of all the dives in Truk Lagoon, this is one that I believe a line reel is mandatory for navigation. Finding narrow exit points in a silt-out can be impossible without one. Pieces of steel disintegrate into a puff of smoke when touched. Visibility seems to always be hazy and deteriorates rapidly every passing minute of the dive. Heavy clumps of rust knocked loose from our venting bubbles rain down from above. The silt inside is so fine that an over-zealous fin kick can cause a plume 6 feet away. For these reasons photography is an after-thought while diving deep in the engine room of the Aikoku. Focusing too much on it can be hazardous under these circumstances. The images in this article took 6 dives to obtain. That is a very low ratio of dives to photos.

Silt OutEven the most gingerly of divers will suffer silt outs like this one in the Aikoku Maru.             Adding to the adrenaline deep inside this eerie wreck are the site of human remains scattered about. On one dive, I clamped off a light and turned it on for a photo opportunity. The powerful beam shined directly onto a skull nestled in the silt about 6 feet away. It was staring directly at me. I quickly adjusted the light and pretended it didn’t happen. Getting rattled in these conditions is not in ones best interest. Many of the human remains were reclaimed by a Japanese dive organization in the 1980’s but it evident that not all were removed. There is rumor that a further reclamation project is planned in the future but I’m not aware of the status.

            The Aikoku Maru lower engine room is the most intense dive in Truk Lagoon; at least it is for me. Although all of the dives and photos obtained in this list required serious planning with high risk to accomplish, I would do it all over again. It was the challenge that made it worth doing.

Special Thanks

          I wanted to say thank you to Eri “Umi” Umino and Keisuke Yokota from Treasures Dive Shop here in Truk Lagoon. Like myself, Keisuke and Umi (which means Ocean in Japanese) were stuck in Truk during the country wide shut down. Together we accomplished some of the most exciting dives in Truk Lagoon and we did so without incident. Both have shown exemplary patience and professionalism. I was fortunate to have divers of their skill level in front of the lens. Thank you Umi and Keisuke! I look forward to future dives together.


            If you desire to dive one of the top 5 most challenging dives in Truk Lagoon, please do not arrive and expect to be able to do so without a lot of pre-planning. For one, most dive operators will not take a diver that has not displayed adequate skills on basic dives prior to attempting these more challenging ones. A certain level of familiarity or comfort level with a diver is required. This takes time; time which most visitors do not have. Contact your operator and see what can be arranged.

            In addition, you will likely need to charter a private boat to bring you specifically to these locations. A dive boat may run into the problem with divers who do not have the skills requesting to follow a team who does. “if they can do it, why can’t I” paradigm.

            Lastly, each of you reading this should be honest with yourself and determine if you have enough experience to conduct technical dives such as these.


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