Pearl Harbor What if?

[hussar62]

Regarding the torpedo attack damage, what was the cause of the misses? I recall that the Japanese had to modify their torpedoes to deal with the comparatively shallow water of pearl (the torps otherwise ploughed into the harbour mud). Has that been factored into your to-hit calcs?

There were multiple reasons for the misses. You are correct in stating some torps hit bottom, others went wide of target and were recovered on the shore line. In one case AA hit the torpedo warhead prior to launch obviously destroying the aircraft. I'm not 100% sure but I believe there may still be undiscovered torpedoes in Pearl Harbor. For mor info you may want to read "Torpedoing Pearl Harbor"

http://www.thefreelibrary.com/TORPEDOIN ... a079586127

[hussar62]

Not trying to be argumentative but it was my understanding that the Fleet would routinely rally in the channel between Molokai and Lanai in peacetime. That would be approximately the same distance as mentioned above but to the southeast. Would this be the case in the event of sortie due to a war warning? Isn't it more likely the fleet would travel to Kahoolawe (the target island) to calibrate and test fire guns? That would be almost another 10-15 NM further to the southeast. Would the Japanese planes have the fuel to reach that much further and does anyone know how much time on target they did have before bingo fuel forced them to return to the carriers?

Thanks for the input sfcmac. In my example I was not so much concerned about the exact location of the US Fleet, just that they had the time to sortie and be approx 60-90 min travel time out side the harbor. I think your dead on about the fuel situatiion on the strike aircraft. I think they were looking at a 360-400 mile round trip and time on target. Not a big margin for doing an extended search if your primary targets are not were you expect to find them. To compond the problem the 2nd wave is already on the way what do you do with them?

[TAMMY]

I have a few comments on the Japanese hit rate. Hussar62 calculated tha verage "overall" hit rate but in my opinion it should be done in detail as follows:

Pearl Harbour. Only 24 torpedo bombers (those of Kaga and Akagi) attacked the battleships. That means 14 hits (2 of the hits wete torpedoes launched by I-16 as shown in 1999) for 24 planes: that means a bit less of the 60%.
On the other side 16 torpedo bombers (yhose of Hiryu and Soryu) made only 4 hits, that is 25%. Overall 18 hits on 40 torpedoes = 45%

Prince of Wales and Repulse. Again indetail we have a forst wave of 16 TB hitting th Prince of Wales with four torpedoes (25%) and two waves of 8 and 26 TB with 2 to 4 hits on Repoulse (7,5% to 15%). Overall 6 to 8 hits withb 50 torpedoes give 12% to 16%.
But in this case we are talking of larger planes than the Kates possibly with more difficulty to hit.

However the main point is not so much how mani hits on moving targets but the effect of the damages to ship on high sea.

For example the Nevada was hit by 1 torpedo and 5 bombs and was groonded to avoid sinking. On open sea this would be a total loss.

The Prince of Wales was hit by four torpedoes but it was the first one to make her sinking. It made important damages including loss of power so the pumps were not able to counter the flooding.

Calòifornia had the same problem of loss of power.

On the overall less damages on open sea owuld have had worst resul on the fleet. It would be inpossible to recover sunken shio.

[robdab]

In my example I was not so much concerned about the exact location of the US Fleet, just that they had the time to sortie and be approx 60-90 min travel time out side the harbor.

I'm sorry that I missed this discussion as the topic has long been a favourite of mine.

I'd like to remind all that Nagumo's Kido Butai carrier strike force was supported by some 29 full sized I-boats historically deployed in Hawaiian waters as well as the 5 IJN minisubs hat tried to penetrate the Pearl Harbor entrance. Their 5 "mothership" submarines had deep water patrol stations assigned just offshore in Mamala Bay, with orders to report any such sortie by the US Pacific Fleet. The remaining 24 were scattered in patrol lines throughout the Hawaiian Islands in order to keep watch/report on the likely USN transit routes.

Also, Yoshikawa, Japan's chief intell officer in Hawaii was based in the Honolulu Consulate which overlooked the Pearl Harbor entrance channel. Had the US Pacific Fleet sortied in the early morning hours of Dec.7'41 he could not have failed to notice such an exodus underway and would have reported same to Tokyo, to be forwarded to Nagumo.

Japanese RDF operators around the Pacific were also monitoring American radio traffic out of PH and had the inbound Japanese attack been detected early, the resulting "spike" in US radio traffic would have alerted the Japanese that their secrecy had failed.

Gorgon Prange's famous book, "At Dawn We Slept" provides much interesting detail on the historical situation on Oahu at the time. He details therein that Genda/Fuchida had historically developed 5 different Hawaii air attack scenarios, the choice of which depended on where the Kido Butai's two cruiser scoutplanes found (or didn't find) the bulk of the US Pacific Fleet earlier on the morning of Dec.7'41. Both Pearl Harbor itself and Lahania Roads were overflown by an IJN marked cruiser scoutplane at about 0700 that morning and Prange reports that after the attack investigation proved that both WERE actually tracked by 3 of the 5 operational US air search radars then located on Oahu. Sadly for those Americans, there were no peacetime manned interceptor warplanes available, no IFF system then functioning nor any manned network of aircraft spotters on the ground on Oahu that could confirm their Nipponese nationalities. Had there been, the American defenders of Pearl Harbor might indeed have had the 1 hour of advanced warning suggested by IRISH.

I think your dead on about the fuel situatiion on the strike aircraft. I think they were looking at a 360-400 mile round trip and time on target. Not a big margin for doing an extended search if your primary targets are not were you expect to find them.

There were still the fixed drydock gates, another floating drydock, several USN submarines under repair/overhaul and many fleet auxilliaries/tankers moored within Pearl Harbor that could have been worthwhile IJN torpedo bomber targets. If it were judged that the available targets were not worth attacking then some of the "long legged" torpedo hauling Kates could/would have been sent in search of the sortieing US Pacific Fleet. The balance of the first wave KB airstrike would have targeted the USAAF airfields on Oahu just as they historically did do.

To compond the problem the 2nd wave is already on the way what do you do with them?

Hit the US Pacific Fleet at sea IF the first wave search planes and/or the IJN submarines find/report them or, hit the 4 American fuel tankfarms located in and around Pearl Harbor and the large civilian tankfarm complex located to the side of the Honolulu Harbor. The 2nd KB air attack wave carried no torpedoes at all and so would not just be wasting it's ordnance loads on American land targets.

[piersyf]

Info regarding the differences between the Pearl Harbour action and the Prince of Wales/Repulse action;

First wave against the Brit ships (torpedo, that is. The first bombers had already made a pass) was made up of 2 groups of either 2 squadrons (approx 17 aircraft) or 2 groups of 17 (text not clear). In any case, PoW was hit twice in the stern but Repulse managed to comb the dozen torpedoes fired at her. Difference then is that the ships were under weigh, not tied up at dock. PoW's hits were in the worst possible place. She lost her rudders, the port propeller shafts, the port turbines and half the ship's machinery (an effect of the turbines running without resistance; they just chewed themselves up). Consequently the after batteries lost power and were unable to train. Those 2 hits did not sink the ship, but put her in a position as if she were tied up; slow and with predictable movement.

The second wave had 2 bomber squadrons and one torpedo squadron. All attacked Repulse as she was still undamaged. All the bombs fell within 100m of the ship, dropped from a height of around 10,000 to 12,000ft. Very good bombing, but none hit. All 9 torpedoes missed as well, as the Repulse again managed to comb the attack. The Repulse's captain, Tennant, signalled PoW that so far he had dodged 19 torpedoes.

Third wave consisted of a single torpedo squadron. This broke up into three flights, one attacking PoW and the other 2 attacking Repulse. This time the 6 against repulse attacked from different angles, making evasion impossible. They still managed to take only a single hit. So far by 12.20 Repulse had dodged 25 of the 26 torpedoes shot at her. The one hit did damage, but she could still make 25kts. Of the three that went on against the PoW, all 3 hit.

Final attack consisted of 3 more squadrons, but not all were needed. One squadron attacked from multiple directions against Repulse, scoring 4 hits from 8 shots (one plane disintegrated from a hit).

Both ships seem to have taken about 5 hits. This may have been excessive, but 1 or 2 would not have been enough for most battleships that are under weigh and with crew at stations to fight their ship.

Primary difference then is speed and maneuver for a ship at sea. True she can't ground herself if sinking, but they are a much harder target. BTW, average run for the torpedoes was 90 seconds at an estimated 40kts if you's like to calculate the release distance.

P

[TAMMY]

piersyf I fully agree with your description aexcepr for some minor details. For example the first wave was of 17 or 16 planes in all, equally divided between PoW and Repulse.

The only comment is about the release distance. The data you give (90 seconds at 40 knots) that is about 2.000 yards, is the maximum range of the Japanese air torpedoes. I suppose that they will try to launch from a lower distance, usually around 1.000 yards obviously depending from enemy AA.

[piersyf]

OK, as I said the description of the first wave wasn't entirely clear, but a total of 16 or 17 I can accept. It may have been narrative license, but the book I have (The Hunting of Force Z) clearly has Repulse dodging around 10 torpedoes. Not a big issue, PoW was hit by 2, Repulse by none.

The 90 second run time was also explicitly stated in the book. Perhaps the Japanese were showing some respect for the guns, given their piecemeal arrival to the fight. The first split attack on Repulse stated that the first flight launched then the second flight waited for Repulse to commit to a line to avoid before the second flight attacked. This left Repulse with no turning options, and also makes the distance/run time less of an issue.

In any case, it's the data I have. I'm sure there will be variations in other sources...

P

[TAMMY]

The 90 seconds (aboput 2.000 yards) is the torpedo run time, that is the time from the launch point to the impact point but give no indication of the launch distance.

You have to coinsier that a ship at 30 knots covers 1500 yards in 90 seonds and the launch is directed to a future point for impact

For example for a launch from the stern you need to relase the torpedo within 500 yards otherwise the ship will outrun it. On the other hand if you llaunch from the bow (supposing a staright route of the ship) you could launch from a maximum distance of 3500 yards. The last is not used as it is the easiest to avoid by the target

Actually the launch distance depends on the angle of approach between plane and what the pilot foresee as manouver of the target but is usually well below the range of the torpedo.