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Ōga Kaiten Replica
Hiji Town [1] , Ōita Prefecture

Ōga was the fourth and last kaiten human torpedo base that was constructed by the Japanese Navy in the latter part of the Pacific War. In 2014, the Hiji Town government implemented several improvements to the former Ōga Kaiten Base area where there still remains more than ten kaiten-related facilities on the former base premises, including underground tunnels to store kaiten and a ramp to transfer kaiten to the sea. The centerpiece of the improvements is a full-size kaiten replica that was put on display in front of the base's torpedo adjustment pool. The local government constructed a large parking lot to accommodate visitor buses, a rest area, and a public restroom.

This historical site excels in information provided about its historical significance. A free six-page color brochure in Japanese is available to a visitor. The brochure has a detailed map of base structures, including photographs of those that still remain. There is also a large information signboard with the following information (translated to English) and a map of the former base.

Historical Background and Kaiten

On December 8, 1941, the Japanese Navy attacked Pearl Harbor at Hawaii's Oahu Island, and the Pacific War began. When the war started the Navy was dominant but shifted to the defensive after the loss in the sea battle off Midway in the North Pacific. Finally, a loss at Okinawa was expected, and air bombardment of Japan's home islands began. As Japan's Navy was in an unfavorable situation, several hundred Type 93 torpedoes dormant in weapon arsenals were modified and employed as human torpedoes that would be steered by a person to make taiatari (body-crashing) attacks against enemy ships. Four kaiten training bases were opened at Ōtsushima, Hikari, and Hirao in Yamaguchi Prefecture and Ōga at Hiji Town in Ōita Prefecture. This human torpedo was named "kaiten" with the meaning of "turn the heavens and reverse the war situation."

Base's Full Details and Ōga Totsugeki [2] Unit

The facilities of this base were expedited in strict secrecy due to the war situation and defensive reasons. They were constructed adjoining the fishing port in Ōga, where Beppu Bay could be used as a training area and where it was geographically superior at the time of a sortie. The base facilities included 51 structures such as the Kaiten Jinja (Shrine), kaiten storage structures, torpedo adjustment shop, transformer substation, and water purification plant. Two thousand men were assigned to the base. The "Ōga Totsugeki Unit" with some 285 kaiten pilots was formed on April 25, 1945. In the same year on August 3, there was the only sortie from this base. Eight pilots and maintenance workers with eight kaiten advanced to Mugigaura on Sukumo Bay in Ehime Prefecture. On August 12, they received an order to stand by to sortie, but the war ended on August 15 without a sortie. On August 25, the Ōga Totsugeki Unit disbanded. The base was handed over to the American military on August 31. After that, kaiten that remained were scrapped. On this base after the war's end, Ensign Shūsuke Matsuo committed suicide.

Present Times

This location of 25 hectares that was Ōga Kaiten Base is nearly all privately-owned land. Cooperation with these individuals is necessary in order to maintain and preserve it in the future.

Hiji Town maintains and preserves the tunnels, torpedo adjustment pool, transformer substation, and water purification pool that remain at present. The town wants to communicate to future generations that a tragic war should never be repeated.

On April 24, 1975, the Ōga Kaiten Association was founded by former unit members. April 25, the date when the Ōga Totsugeki Unit originally was formed, was set as the date of the regular festival that is held each year.

We will be pleased if everyone who visits this place will realize personally the preciousness of people's lives and the blessings of peace.

Human Torpedo Ōga Kaiten Base Site Monument

On the road approaching the kaiten replica there is the above monument with the engraved words of "Human Torpedo Ōga Kaiten Base Site Monument." The monument's base has a plaque with the following words:

Turn the heavens hoping to reverse the war situation.

October 2011
Donated by Hiji Lions Club

Former kaiten storage tunnel

The information sign directly in front to the kaiten replica has the following information:

Length: 14.75 m, Diameter: 1.0 m, Total weight: 8,300 kg
Maximum speed: 30 knots (about 56 km/hr), Cruising time: 2 hours, 15 minutes (at 12 knots)
Warhead weight: 1,550 kg, Crew: 1 man

On April 25, 1945, Ōga Kaiten Training Base opened. From May 23 training started in the training area in Beppu Bay. In the training the Type 1 Mod. 1 kaiten, which was an improved version of the Type 1, was used. The most significant differences compared to the Type 1 were a modified shape to better cut through waves and the ability to make a sortie from land without a hatch on bottom to enter from a submarine [3]. On August 3 near the war's end, there was the only sortie from Ōga Base. Eight Type 1 Mod. 1 kaiten and eight men went through dangerous seas and made it safely to Mugigaura on Sukumo Bay in Ehime Prefecture. They received an order to stand by to sortie, but while on stand-by the war ended.

Information signboard with map of Ōga Kaiten Base

To the right of the kaiten replica there is a small monument to remember those who contributed to the creation of the display. The inscription reads:

Monument Honoring Human Torpedo "Kaiten" Replica Creation

This location was a kaiten training base. Base preservation activities are carried out to communicate to future generations the tragic war history. The creation and set-up for display of a full-size kaiten replica has been accomplished through the support of volunteers in the area. Here we express our gratitude by recording the names of persons from whom great cooperation was received.


Heiseikai Medical Corporation
Kiminori Sakai, Chairman

Shōwa Kensetsu Kōgyō
Kensaku Endō, Chairman


Matsumoto Shōten
Shōjirō Matsumoto, Representative Director and President

March 2014
Yoshimi Kudō, Hiji Town Mayor

Kaiten replica next to former torpedo adjustment pool

The Ōga Kaiten Shrine on the grounds of Sumiyoshi Shrine is located a short distance from the kaiten replica on the top of a hill overlooking the bay.


1. Ōga Village was merged into Hiji Town in 1954.

2. The word totsugeki means "charge" or "assault" in Japanese.

3. The hatch for the Type 1 Mod. 1 kaiten was on top rather than bottom.