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Maritime Archaeology/Marine Heritage

Japanese midget submarine: sunk Dec 7, 1941 - found, Aug 2002

Painting by Terry Kerby

Painting (acrylic on canvas) by Terry Kerby, HURL's operational director and chief sub pilot

Analysis of Hole in Conning Tower of Midget Sub
update as of 12/20/2003

The Search for the World War II Japanese Midget Submarine Sunk off Pearl Harbor, Dec. 7, 1941

John C. Wiltshire, Ph.D.
Hawai‘i Undersea Research Laboratory
School of Ocean and Earth Sciences and Technology
University of Hawai‘i, Honolulu

(click to view images)

Introduction

At 12.20 p.m. on August 28, 2002, the Pisces IV and Pisces V, two deep diving submersibles operated by the Hawai‘i Undersea Research Laboratory (HURL), found the Japanese midget submarine which was the first vessel sunk in the attack on Pearl Harbor, December 7th, 1941. HURL is one of six national laboratories comprising NOAA's National Undersea Research Program. It is located at the University of Hawai‘i's School of Ocean and Earth Sciences and Technology. The sunken midget sub was located during the last of a series of test and training dives conducted annually in the military debris fields off Pearl Harbor. HURL is now undertaking its regular four to five month dive season of scientific and engineering dives focusing on fisheries enhancement , coral reef habitats, undersea volcanism, landslide monitoring, acoustic identification of fish and their habitats and other engineering and oceanographic studies.

This midget sub find has been described as the most significant modern marine archeological find ever in the Pacific, second only to the finding of the Titanic in the Atlantic. The Japanese midget sub was one of five attached to five I-class mother submarines and brought from Japan to be launched 5-6 hours before the aerial attack, within a few miles of Pearl Harbor. Each had a crew of two. The subs were battery powered , 78 feet long , 6 feet in diameter and weighed 46 tons. They carried two torpedoes and a scuttling charge to avoid capture. Although experimental in design, they were very advanced for the time. For short periods, they could run at 20 knots. These midget submarines were completed only months before the attack allowing little time for the crews to train. All of the five submarines comprising the advanced attack force were sunk or captured. The type A midget submarines had a series of basic design problems including trim and ballast control and problems both with battery life and battery monitoring. Later redesign, as five man midget submarines of the Koryu class, addressed but did not solve these problems. The Japanese midget submarines although believed at the time to be a potent secret weapon, in actual fact, were never highly effective. So far four of the five original midget submarines attacking Pearl Harbor have been found.

History

The discovery of the midget submarine confirms the account radioed to naval command at Pearl Harbor at 6:45 am on Dec. 7, 1941 . A Japanese submarine was shot through the conning tower and then depth charged trying to enter Pearl Harbor behind the USS Antares. The crew of the attacking USS Ward , an older style four stack destroyer, saw the midget sub lifted out of the water by depth charges after firing the fatal shot from its four inch side gun. The Ward's crew were Naval reservists from St. Paul, Minnesota. Unfortunately, Naval command in Pearl Harbor ignored the Ward's report and the aerial attack began at 8 am. At the Pearl Harbor investigation, some question was made of the accuracy of the Ward's report. The Ward is now vindicated. The Ward itself was later targeted by the Japanese and sunk in a kamikaze attack, ironically on Dec. 7, 1944, in the Philippines.

Search

The search for the Japanese midget sub has been ongoing for 61 years since it was first sunk. In its latest phase, the Hawai‘i Undersea Research Lab has conducted towed side scan sonar surveys of the debris fields off Pearl Harbor. At the end of World War II, obsolete war material was dumped in 1,000-3,000 feet of water several miles off Pearl Harbor. This included: landing craft, tanks, old aircraft, trucks, barges, small ships, fuel tanks etc. There are on the order of 1,000 significant sonar targets in the area. Sorting through these various targets to identify the most promising ones to dive on as a submersible pilot training exercise has been the work of many years. The Japanese midget submarine although giving a very clear return on the side scan survey was interspersed with other debris on the bottom complicating the search efforts.

Findings

The Japanese midget submarine was found in 400 m of water about five miles off the mouth of Pearl Harbor. As it is an historically significant military vessel and (per agreement with the government of Japan) a property of the U.S. federal government, its exact location is being protected by the U.S. State Department and heritage resource management agencies. The submarine sits upright on the bottom and is in amazingly good condition as shown in the photos. Both torpedoes are still in place. The submarine has no apparent depth charge damage but does have shell damage on both sides of the conning tower. The port side of the conning tower exhibits what one analyst has identified as shrapnel holes. This would presumably have come from the first shell fired by the USS Ward which exploded near the submarine but did not directly hit it. The starboard side of the conning tower shows a hole from the 4 inch shell fired by the side gun on the Ward as the ship steamed past. Apparently, this shell did not explode on impact as the midget sub conning tower is clearly still in place. While four depth charges were dropped directly on the midget as the Ward passed by, the charges were set to go off at a depth of 100 feet and the submarine was at the surface. The pressure wave created by the 4 depth charges was sufficient to fully lift the 46 ton, 78 foot midget out of the water, but did no visually apparent structural damage. The midget sub sank from flooding through the four inch shell hole.

Questions

A number of questions still remain over this submarine, which was the first casualty in the war between the U.S. and Japan. Why did the Naval command at Pearl Harbor apparently ignore a confirmed enemy sinking right off its harbor mouth? Why did the Japanese put so much faith in the five midget submarines that they were allowed to lead the Pearl Harbor attack? After all five of the attacking midget submarines were lost in their first engagement and shown to be ineffective, why did the Japanese Imperial Navy go on to build hundreds of midget submarines most of which were never used? Regarding the site and vessel itself: Should it ever be raised? What is its structural integrity and deterioration rate? How stable is its position on the seabed? How can we best learn from the site and preserve it for future generations?

Heritage Preservation and the Future of the Midget Sub

Since its discovery, the Japanese midget sub has become the focus of a concerted research and preservation effort on the part of HURL, NOAA, and the National Park Service. Resting in the darkness on the seafloor, the site is a tangible reminder of historic events which began the war in the Pacific, and as a war grave a monument to the sacrifices made at that time. The midget sub is most directly connected to the Pearl Harbor National Historic Landmark and the unique sites of the USS Arizona and the USS Utah. Careful preservation and study of the sub is, therefore, well warranted. NOAA's maritime heritage management efforts feature in situ preservation as the preferred alternative. This approach does not ultimately prohibit intervention or even recovery, but instead emphasizes the precautionary approach and the need for data collection and fully understanding the unique resource prior to taking any action that might detrimentally impact the site. The goal is heritage preservation and resource protection so that future generations may learn from and appreciate our maritime past. To this end HURL, NOAA and the National Park Service have entered into a joint agency collaboration and are in the process of gathering appropriate data on site environmental conditions, metal deterioration rates, and stability status of the midget sub. This is an essential step in the long term heritage management plan for this special property. All research actions are taken with proper regard and respect for the site's historical significance and war grave status.

As we learn more about what will become of the Japanese midget submarine, we will post it on this website.
All images are the property of the HURL Data Dept. Please contact Rachel at 808-956-6183 if you would like to work out an agreement to use any photos or video of this midget submarine. Please be aware that there will be a fee involved.

The following 5 images are mosaics produced from images grabbed from video
shot on the first dive to the Japanese midget submarine. (Credit: Terry Kerby)
Mosaic image of the midget submarine Mosaic image of the midget submarine
Mosaic image of the midget submarine Mosaic image of the port side of the midget submarine
Mosaic image of the midget submarine Mosaic image of the midget submarine
Mosaic image of the starboard side of the midget submarine Mosaic image of the bow of the midget submarine
Mosaic image of the midget submarine
Mosaic image of the stern of the midget submarine
The remaining images were taken with a digital camera on the first dive to the Japanese midget submarine.
Pisces IV by the stern of the midget submarine Japanese midget submarine
Pisces IV by the stern of the midget submarine Japanese midget submarine
The bow of the midget sub with the two torpedoes intact The conning tower of the midget sub
The bow of the midget sub with the two torpedoes intact The conning tower of the midget sub
Port side of the conning tower -- note the two small holes. Closer look at the port side of the conning tower.
Port side of the conning tower -- note the two small holes. Closer look at the port side of the conning tower.
Starboard side of the conning tower -- note the hole. Closer look at the starboard side of the conning tower.
Starboard side of the conning tower -- note the hole. Closer look at the starboard side of the conning tower.
Stern (back) of the midget sub. Closer look at the stern.
Stern (back) of the midget sub. Closer look at the stern.
Pisces V shining light on the bow of the midget sub. Pisces V shining light on the conning tower of the midget sub.
Pisces V shining light on the bow of the midget sub. Pisces V shining light on the conning tower of the midget sub.

 

 

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