Mini Subs at Pearl Harbor??

[GrauGeist]

Midget Sub #1 was shelled by the U.S.S. Ward, over an hour before the Japanese warplanes attacked. It remains where it sank, just outside the harbor.

Midget Sub #2 entered Pearl Harbor, but after missing its target with both torpedoes, the sub was destroyed by a pair of American ships. It was raised two weeks after the attack and buried as landfill.

Midget Sub #3 ran aground on the east side of Oahu, its captain became the first Japanese prisoner of war. Neither of its torpedoes had been fired. It is now on display in Texas at the National Museum of the Pacific War.

Midget Sub #4 turned up years later, several miles south of Pearl Harbor found in 1960, at Keehi Lagoon, and it still had its torpedoes in it. That midget submarine was shipped back to Japan and now stands outside the Naval Academy in Etajima.

Midget Sub #5 was recently found three miles south of Pearl Harbor in a pile of wreckage. It is believed that after the attack, the sub ended up stranded in an area of the back bay, called the West Loch near Waipoio penninsula. After being stranded there for several years, it became buried by debris during a disaster that happend in 1944 during the transfer of ammunition aboard an LST. Several hundred sailors were killed and injured and 6 LSTs were sunk...all on top of the midget sub. When they cleaned up the wreckage, the sub got scooped up with the debris and dumped out at sea. During the investigation, they found the topredo tubes to be empty. The control room of the Midget Sub is still sealed and it is believed the two crewmen may be aboard.

Here's an annotated photo of the one I posted above showing the diagnostics of the sub's attack:

 

[dutchman]

I've seen the map of Pearl Harbor on Dec 7th showing the position of the ships before the attack. Does anyone know where the carriers would have been if they had been in port????

 

[Thorlifter]

I don't know GG. I'd love to think a moment in history was captured the millisecond before the explosion, but I ask this. If we can assume that the first torpedo fired is the longer track headed towards the West Virginia, that would mean it would have to swing to fire its 2nd shot towards the Oklahoma. If that's the case, why is the "rectangular shape" aligned with the 1st shot?

If your answer is because it was starting it's turn out of the harbor, I find it hard to believe it would be perfectly lined up with the 1st shot.

I still tend it believe torpedoes were dropped by two planes and the torpedoes entered the water to the left of the mark you called "rooster tails". You can see their splashes in your first picture. The torpedoes could have porpoised causing the rooster tails. If my guess is correct, the Kate's would have been far out of the picture by the time the image was taken.

Also, it's my opinion the spot you marked are rectangular object is a flaw in the picture. It almost has a hard edge to it and everything else is a soft, almost blurry edge. But I'm no expert in object identification on 70 year old black and white film.

 

[Matt308]

I agree, Thor. These pics are subject to much debate. There has been many "experts" making claims of facts over these photos and best I can tell, nothing has been proven definitive.

 

[parsifal]

but I ask this. If we can assume that the first torpedo fired is the longer track headed towards the West Virginia, that would mean it would have to swing to fire its 2nd shot towards the Oklahoma. If that's the case, why is the "rectangular shape" aligned with the 1st shot?

That is not necessary. all WWII subs had a TDC, basically an analog computer into which bearing, range, target speed, and for more sophisticated computers, things like current and wash, could be fed in and estimates made for the torpedoes gyro setting. The second crewman would then adjust this before firing, for some more advanced torpedoes, its speed and pre-ignition settings could also be made.

There is no real technical difficulties to torpedoes being fired simultaneoulsy on diffrent headings

 

[GrauGeist]

The annotated image is not mine, I've had it for some time on my drive. I have always been curious about the matter and have tried to find a copy of that image with a higher resolution. The photo was taken from the air during combat, so that's probably as good as it'll get.

The fact remains that they did find the 5th mini sub after all these years and they did confirm that it did launch it's torpedoes before coming to rest on the bottom of Pearl's back bay before disaster in 1944, eventually being scooped up and dumped to sea with the LST wrecks.

 

[dutchman]

I agree that most subs could fire on multiple bearings, Firing a "spread" of torpedoes was common. I can understand the tower of the sub being their after the shot. The captain is going to watch the track as there is too much noise to confirm his hits. To be truthful, these crews knew they were on a one way ticket. Watching the hits would not be unreasonable. If there was much chance of making it out and home they would have submerged and evaded. As it was no one may have seen them anyway for 60 years or more as we still can't agree if the photo shows a sub.

 

[GrauGeist]

The mini subs carried 1,000 pound torpedos...these were twice as heavy as airborn torpedoes. Launching from the mini sub would have caused the sub to violently "kick back", momentarily lifting the stern from the water. In addition to that, these early mini subs had a small rudder, making them difficult to manouver.

There was a report filed after Pearl Harbor that stated a large torpedo was found unexploded, but there is debate on a large torpedo strike on the West Virginia, which caused significant damage. This would be in keeping with the torpedo wakes seen in the photo.

 

[Shinpachi]

The bow is said jumped up in experiment and it made the mini sub unstable for the immediate second shooting.

 

[GrauGeist]

The bow is said jumped up in experiment and it made the mini sub unstable for the immediate second shooting.

Which is why the second torpedo most likely ran wide of it's target and ended up beaching. It was recovered after the attack, Admiral Nimitz made a mention of the torpedo finding in his congressional report.

 

[Thorlifter]

I am certainly not saying you're wrong. In fact, I want to believe it and it would make the picture even more amazing. I guess I'm just getting too cynical in my old age.

 

[dutchman]

The reaction of the mini sub when launching a torpedo would be somewaht violent. Once fired the sub would "recoil" from the launch which could make the stern rise. Then once the torpedo had cleared the tube you would be faced with a terrible weight shift to compensate for. The bow just became 1500 pounds or more lighter. So it will of course rise. To keep it under control would be a major effort. It would be a bit of a bucking bronco ride for the crew. I do know you can't fire the two torpedoes at the same time. That could have terrible results. I would guess and I say guess it would be 45 sec. before a second the torpedo could be launched.

 

[Shinpachi]

Local wiki says,

The Ko-hyoteki (mini sub's code name which means 'Target-A' ) was equipped with two torpedoes in its nose end. Type 97 oxygen torpedo with a diameter of 45 cm was used initially till the Battle of Solomon Islands (Guadalcanal) from the outbreak of the Pacific War. Shooting range was 5,000 m with speed of 50 knots.

After Type 97, Type 2 or Type 91 torpedo of 45cm diameter was used. Range was 3,900 m with speed 39 knots. These electric drive types showed superior maintainability to the oxygen type. Explosive charge weight was 350 kg for both types and the firepower of a Ko-hyoteki was equivalent to two attackers of aircraft.

A pair of torpedos were housed in launch tubes and emitted by injecting air to the tube. Buoyancy of nearly 1 ton occurred when a torpedo was released. The bow bounced and jumped out to the water surface. Because of this unstable behavior, torpedo was shot out in the biased direction and did not necessarily catch the aimed target. It was about 30 seconds till stabled again.

As the second torpedo was unable to be directed to the correct direction in such an unstable state at all, they could not adopt the ordinary tactics of putting enemy in sparging torpedos but performing single-shot shooting only. Optimum shooting distance to the enemy ship was said 800 m.

...............

I am unable to understand why the buoyancy was nearly 1 ton.
So, Please don't ask me.
Thanks!

 

[Wayne Little]

The referenced photo of battleship Row was apparently taken by Lt. Hirata Matsumura's navigator, Petty Officer 1st Class Takeo Shiro as they banked away from their aborted torpedo run on West Virginia, the photo shows Petty Officer 3rd Class Yasumi Oku's torpedo hit on West Virginia with the initial wave blast close against the ship, keen eyes will spot the beginning of the large water spout about to erupt into the air from the torpedo hit.
Matsumura circled around and dropped back in between Akagi and Kaga's attack formations to release his torpedo also striking West Virginia.
Matsumura was the Second in command of the Torpedo attack in command of Hiryu and Soryu's torpedo bombers flying aircraft BII-320, while Oku's aircraft was BII-302 these pilots redirected their attacks on to battleship row from their assigned targets, slotting into the stream of Akagi and Kaga torpedo aircraft, and not wanting to waste their torpedoes on a lesser target than a Battleship.
The attack on battleship row by the torpedo aircraft was completed in a rather short duration of approximately 10 minutes during which some 27 aircraft attacked the ships, not all released their torpedoes, a few of the final Kates from Kaga were shot down before releasing their torpedoes, however some 20+ torpedoes were dropped in this short space of time providing plenty of torpedo wakes, waves and explosions in the waters of Pearl Harbor and this is more likely what can be seen rather than a mini sub.....

 

[dutchman]

Okay folks here's a crazy idea. What if the Pearl Harbor attack was conducted differently. There are many things about the attack on both sides that bother me. But, with the advantage of hindsight that might be to easy to say. Now please don't take offence with this I'm not trying to start trouble I just want to look at this from a professional point of view without too much emotion.

The attack was planned by some of the most brilliant minds in the military, so here's a point. Why mini subs at all? If you send 5 mini's in with a total of 10 torpedoes, do you really think that will tip the scales when you are about to hit with over 340 aircraft and drop 40 torpedoes and a almost a hundred bombs? I would think that the risk of one of the 5 subs being discovered and raise the alarm would outweigh any good they could have done during the attack.

Why not modify the mini subs. They carried 2 torpedoes, remove one and replace it with a huge high capacity air tank. This should allow the mini to remain submerged for at least 36 hours. These mini subs could have made it into the harbor as at least one did. And then pick a point away from the ships and bottom the boats and wait. Let the planes do their thing. Then at a prearranged time say 0100 on Dec 8th slowly surface and look for targets of opportunity. The Enterprise would have been back in port by then. If the battleships were down and a carrier took 1-2 torpedoes in the side, it could be laid up for several months if not sunk. It would also have caused much confusion to the rescue and repair efforts if they weren't sure the harbor was safe. Much the way a bomber formation would drop a percentage of bombs with time delay fuses.

I was reading a report that claimed the attack was not as successful as they had hoped. The accuracy was less then expected. By about 20% with the bombs and a little more with torpedo. But you know the attack seemed sucessful enough to me!!!!

 

[GrauGeist]

To commit assets to the attack, you want to have them have as much ordnance as possible to make the effort a success. A mini sub with a single torpedo cuts thier chances in half before they even start thier mission.

As it stands two made it into the harbor, one was caught and sunk, the other (#5 mentioned above) at least deployed it's torpedoes. The idea of mini subs supplementing the attack was to inflict the maximum amount of damage while they had the element of surprise. Nagumo called off the third wave when he saw that Pearl's defenses were more than they had counted on.

The Americans may have been caught sleeping, but they didn't take long to put up defensive fire. The other factor in Nagumo's decision, was that they didn't know that the carriers and thier support ships were out to sea. They had counted on the bulk of the fleet to be tied up that morning.

 

[dutchman]

I understand that the mini subs were a minor factor in the battle. They carried a total of 10 torpedos but were only able to fire 2 torpedos at a maximum, one of which may well of missed it's target. So reducing to one torpedo per mini sub wouldn't have reduced the combat effectiveness of their portion of the attack much if any. There was speculation that they might have been trying to sink any vessel attempting to leave and by doing so plug the channels of the harbor. That would have closed it down for many weeks if it were a large ship.

They did realize the carriers might not be there. The target assignments were complicated but navy command wanted the battleships as first priority. Genda who designed the attack saw battleships as obsolete and wanted to move the carriers to the top of the target list. There was also much effort to reduce duplication of hits. But the attack broke down and confussion set in. Many of the ships had more attacks then they were suppose to some had less. After the Battleships, the Carriers were next in their absence the Cruisers took the remander of the firepower.

 

[GrauGeist]

The subs may have been more of a contributing factor, but too many things went wrong and only one made it to an attack position.

Had all 5 made it to thier designated positions and delivered all 10 torpedoes, this may have contributed to more destruction. The larger torpedoes had a significant destructive power over their airborn counterparts.

These early mini sub types had several problems which were addressed shortly after Pearl Harbor...one of the main problems being the rudder, which was too small.

 

[Wayne Little]

I was reading a report that claimed the attack was not as successful as they had hoped. The accuracy was less then expected. By about 20% with the bombs and a little more with torpedo. But you know the attack seemed sucessful enough to me!!!!

Whilst i can't say much on the percentage for Bombing accuracy, the torpedo Accuracy was reasonably high from 40 torpedo aircraft, off the top of my head I can count at least 26 of 40 torpedoes hitting targets less 3 of 5 I think that were shot down without releasing torpedoes 26 of 37 does give a reasonable percentage of hits. now one would expect a pretty good accuracy count, the targets were stationary, and AA fire didn't react until more than half had dropped their torpedoes, once they got to firing, 5 of Kaga's last 7 aircraft to attack were shot down.

 

[parsifal]

Why not modify the mini subs. They carried 2 torpedoes, remove one and replace it with a huge high capacity air tank. This should allow the mini to remain submerged for at least 36 hours. These mini subs could have made it into the harbor as at least one did. And then pick a point away from the ships and bottom the boats and wait. Let the planes do their thing. Then at a prearranged time say 0100 on Dec 8th slowly surface and look for targets of opportunity. The Enterprise would have been back in port by then. If the battleships were down and a carrier took 1-2 torpedoes in the side, it could be laid up for several months if not sunk. It would also have caused much confusion to the rescue and repair efforts if they weren't sure the harbor was safe. Much the way a bomber formation would drop a percentage of bombs with time delay fuses.

Japanese mini subs were designed as nuisance weapons only, and in this role were reasonably successful. Even when no observable results were the only result, this can be argued to be a good outcome. typically, following a nuisance raid there were extraordinary defensive measures that needed to be taken by the defending naval force across an entire region. The British experiences in the Med against the X MAS flotilla are typical. Despite the fact that X MAS delivered less than 5 successful attacks overall, the British throughout the Med were forced to adopt draconian and costly harbour defence procedures that also tied up large numbers of personnel and even quite a few ships. For the investment in men and materrial by the attackers, min sub operations were generally very good at tying down larger amounts of enemy resources. Japanese minisubs were in this category.

Following the Japanese attack at Pearl, the whole area went into complete lockdown, with ASW netting, active patrols, shore patrols, you name it. It would have been imposasible for a Japanese vessel of any size to lie undetected within the harbour. even the subs lying offshore had a hard time of it after the attack.