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Topic: Recovery Plan 1, The Lanai Island rendezvous< Next Oldest | Next Newest >
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Ken Hackler Search for posts by this member.


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PostIcon Posted on: Jul. 28 2002,12:34   Ignore posts   QUOTE


The five midget submarines used by the Imperial Japanese Navy as part of the Pearl Harbor attack have been largely overlooked by history. In reality, the midget submarine aspect of the attack was just a tiny portion of the overall plan, which was essentially a massive air strike.

The midgets were launched from specially prepared fleet submarines, called "mother" submarines. Once launched, the midgets had to find their way into Pearl Harbor in the dark, lie in wait in the channel until the air attack began, then make their way into Pearl Harbor proper to attack American battleships.

After making their attacks, the midgets had the daunting task of trying to leave Pearl Harbor. In reality, that was a suicidal mission because they had no hope of getting out of the harbor again once the U.S. Navy was alerted. However, they did have three plans for recovery of the midget submarines and the ten crewmen.

The first and primary plan was as follows:

Once they escaped from Pearl Harbor, the midget submarines were to head east southeast (ESE) to a location about 7 miles off the west coast of Lanai Island. The crews would be rescued by their mother submarines at that point, even if the midget submarines could not be recovered.

Since all but one of the midget submarines was lost in the attack, as well as all the crewmen but one, we have only general information about the recovery plans. Senior Japanese Navy officers who survived the war filled in some of the blanks, and the lone survivor of the midget submarine crews helped fill in the rest. We can, with some confidence, infer that all the midget submarine crews had similar plans to go from Oahu to Lanai Island, since there are really few navigational alternatives.

Kazuo Sakamaki was captured on the morning of December 8, along with his boat. He did not say too much, but the items found inside his boat spoke volumes. Two navigation charts were recovered in his boat, one large-scale chart showing the approach to Oahu, and another, smaller-scale chart, that showed Pearl Harbor itself. Interestingly, there was no chart of the Hawaiian Islands that showed the trip from Oahu to Lanai Island. How then did Sakamaki intend to get there? One of the reasons there was no other chart was (I think) a matter of security. If a midget had been captured, a chart would have shown the U.S. where the rendezvous location was, and the Japanese would have been worried about that.

The answer is that Sakamaki did not need another chart. Amongst the items found in the boat were a navigation instrument that was known as a "double-mirror" when translated, as well as a "chart of distances."

The "double-mirror" was mentioned by LCDR Edwin Layton when he testified before the Hewitt Inquiry, although he referred to it by an older slang term of "palm and needle." The question is, was it a sextant or a stadimeter? Both instruments use "double mirrors" to function.

A sextant is a navigational instrument that measures the angle of a celestial body, such as a star or sun or moon, above the horizon. Once the angle is established, the person doing the calculations spends an hour or two going through voluminous books to find the right position. When three or four such fixes are obtained, the position of the vessel can be established. As you can see, this is very time consuming and difficult.

However, there were no books found in Midget C that would have allowed Sakamaki to establish his position once the star angles were taken. Why then would he have had a sextant? It was of no use.

But a stadimeter, on the other hand, was perfect. It does not establish an angle above the horizon of an object, but rather, it establishes the distance of an object from the person taking the sighting. It does this by knowing in advance what the height of the object is above sea level.

This makes perfect sense. Sakamaki's boat had a "chart of distances" when recovered. Although the description is not terribly detailed, one can assume that the "distances" on the chart were in relation to some fixed object, such as an island or a prominent physical feature on an island such as a mountain. A distance is only of any value if it can be related to something easy to see or locate.

Knowing this, Sakamaki's plan makes a lot of sense. He had a chart that showed him passing about 4 miles south of Diamond Head on a course of 107 degrees. This would, on the face of it, seem silly, since a course of 107 would run him into the western end of Molokai Island about 18 miles north of where he wanted to be.

Yet keep in mind the very simple and rudimentary type of navigation Sakamaki had to do. Going across the channel between Oahu and Molokai on a course of 107 degree meant that Sakamaki was crossing at the narrowest point of the channel. Less open ocean to cover, and therefore less potential error in his navigation. He had physical features behind him to aid in his navigation, because he could see Diamond Head through his periscope until he was well over halfway across the channel. From that point, he had the mountains of Molokai Island in front of him to see. Very simple navigation. It worked well in 1941, and it still does today.

All he had to do was steer a course of 107 degrees toward Molokai Island until he reached the point where he had to turn southeast towards Lanai. But how was he to know when he reached that point? Simple - he had a stadimeter that he could use to sight on a mountain with a known height on Molokai, such as Mauna Loa, and when the stadimeter told him he was within a certain distance of that object, Sakamaki would change to a new course to the southeast that took him to the rendezvous point near Lanai.

I have laid out what I think is a probable track - an intended course - using the known facts. For example, we know from the captured charts that Sakamaki intended to leave Oahu on a course of 107 degrees. He also intended to pass about 4 miles south of Diamond Head. We know where he was going, and we know he had a stadimeter.

Laying out the track to the western tip of Molokai was simple. By the way, there was a navigation light on the western end of Molokai that Sakamaki could have seen for about 7 miles with his periscope if he'd been delayed in his departure from Oahu and arrived at night. However, the early morning (1000 - 1100) departure time meant that he would arrive just before sundown if he kept to his intended speed of 4 or 5 knots.

He would have navigated straight across the channel between Oahu and Molokai by sighting off of Diamond Head and Mauna Loa. At some point, perhaps just past halfway across, he would have surfaced the boat long enough to take a sighting on Mauna Loa with his stadimeter. That would tell him how far he was from Molokai Island, and how far he had to go to reach his turning point. He would then continue on course, without changing speed or direction, for the time necessary to reach his turning point.

As I have it laid out, the simplest choice for turning would have been when Mauna Loa was 090 degrees true from Midget C, because the turn to starboard to put him at the rendezvous was 045 degrees. His new course was 135 degrees. It doesn't get any simpler than using Cardinal headings. No charts are needed, just a few notes on a piece of paper giving the "distances", which we know Sakamaki had.

When he continued along the second leg of his journey on a course of 135 degrees, all Sakamaki had to do was keep an eye on the time and his speed to know when he was approaching the rendezvous point. It would have been pitch black outside when he arrived, but the midget submarines had three ways to contact their mother submarines once they got close.

First, they had a radio. That is the obvious method of contact. They also had flashlights for visual signals. Lastly, the midget submarines had a fathometer. It was a simple sonar device that emitted a loud "ping" which the mother submarine would use to locate the midget and give directions.

All of this may seem complicated to someone who is not familiar with navigation in the ocean, but it is the simplest and most basic form of navigation. It also works, and these basic practices have been used for centuries. They are still in use today, even though we have electronic devices to assist us now.

That explains what I believe was the primary plan for recovery of the midget submarines based on the known facts and a little bit of experience in navigating ships. There may be other solutions that work as well, but I think this is pretty darned close.

The two alternate recovery plans will be discussed in other posts.

Edited by Ken Hackler on --

Ken Hackler
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