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American Forces Press Service

Scientists Clarify 'Mini-Sub' Role at Pearl Harbor

By Judith Snyderman
Special to American Forces Press Service

WASHINGTON, Jan. 8, 2010 – Scientists who have been studying wreckage from Japanese mini-submarines that were part of an advance strike force on Pearl Harbor on Dec. 7, 1941, say a new television show is informative, but could leave viewers with misunderstandings.

For one thing, they say, the show -- part of PBS’s “NOVA” series -- reveals no new discoveries.

“It's basically a synopsis of the work that we performed up through 2000,” Navy Capt. John A. Rodgaard said during a “DoDLive” bloggers roundtable Jan. 6. Rodgaard was joined by Peter Hsu, a scientist who analyzes forensic shock effects of underwater explosions, and Robert Neyland of the Naval History and Heritage Command, which studies shipwrecks and sunken aircraft.

These experts say there’s no dispute that hours before the main air attack on Pearl Harbor, the Japanese navy launched five mini-subs armed with torpedoes from larger submarines. U.S. Navy ships sank the mini-subs, and the first pieces of wreckage were identified by the Hawaiian underwater research lab called HURL in 1992.

Another key piece of evidence is an aerial photograph of one of the mini-subs that was taken by a Japanese aircraft.
In 1994, Rodgaard used that evidence to correct earlier beliefs that only one of the five submarines that had been launched made it into the harbor, and that it failed in its attack.

“What we demonstrated initially was that a second one had actually entered and also was successful in its attack,” he said.

The mini-sub pictured in the aerial photograph is the one featured in the television documentary, Rodgaard explained. But the show implies the wreckage is a new find, he added, when it actually was well known for years, though it wasn’t identified as one of the five Pearl Harbor attack mini-subs until recently.

Neyland said the timeline presented by the program incorrectly suggests the sub was the last of the five launched. “We consider that the No. 1 submarine, based on the Japanese records of the release times,” he said.

One other problem, Rodgaard said, is the documentary’s assertion that a mini-sub torpedo struck the USS Arizona and did not detonate.

“I don't know about you, but I don't think an object such as a torpedo that winds up being a dud, striking an object at [42] knots, is going to remain intact,” he said. Hsu theorized that, based on weight analyses, the unexploded torpedo depicted on the show may have been dropped from an aircraft.

Despite these concerns, the experts agreed that the story of the Pearl Harbor mini-subs is a fascinating piece of history that deserves ongoing research. One mystery is the location of the wreckage in a 1,000-foot-deep debris field outside Pearl Harbor. Neyland said it’s clear the mini-sub must have been salvaged after the war ended, but that leaves unanswered questions, such as why it is where it is, why it is disassembled, and why no record exists of it having been found and salvaged out of Pearl Harbor.

Rodgaard added that a 15-foot section of the mini-sub is missing, and he hopes it will be found. Each piece of evidence is a time capsule of history, he said.

Scientific techniques such as bio-corrosion studies on bolts and studies of the origins of microorganisms attached to parts may solve some of these mysteries. “I would say our journey continues,” he said. “There are quite a few things that we could still do.”

(Judith Snyderman works in the Defense Media Activity’s emerging media directorate.)

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