Pearl Harbor - warning - what ATL difference.

[merlin]

I'm not talking maybe up to an hour - with the radar warning.

I'm not talking about an hour plus, - I want confirmation' of the submarine sighting by USS Ward

Nor am I talking about the final decrypt that led to the final warning - if someone for example realised what the significance of the time stipulation was.

No, I'm going back to August 1941 when Double-agent 'Popov' was interviewed by Hoover himself at the FBI. 'Popov' was sent to the US under instructions from the German Secret Service, he was meeting the FBI under the instructions of the British Double XX Committee.
A big part of Popov's brief was to get information on Pearl Harbor defences - for example torpedo nets - were they used, when etc. He had information on the Japanese interest in the British RN attack on Taranto - the Japanese visited the base.
Hoover showed no appreciation of the significance of the line of questions, or wondered why the interest. He seemed more morally offended by Popov who he regarded with some distaste as a 'playboy' ready to pass on US secrets too the Germans. He only seemed interested in the new German technique of Micro-dot technology., which he reported to FDR - but nothing about the interest in Pearl Harbor.

But, what if he did grasp the significance, and realised that an attack by the Japanese was being planned. What then? There don't know when, or how - what direction.
There is still scope for 'cock-ups', they can't go on alerts continuously! Presumably there will be recon flights, submarine patrols
OTOH IMHO they don't want to arose any suspicion that they 'know', but they need to be able to give the Japanes a warm welcome when they do arrive, though the Zero will still be a surprise.
What's next?

 

[Hereward the White]

I seriously doubt JEH would've even considered the implications, seeing as he couldn't tell the difference between a spy and a criminal. According to Ben Macintyre he saw double agents as 'fly paper', nasty to handle but good for catching 'vermin'.

 

[Glenn239]

But, what if he did grasp the significance, and realised that an attack by the Japanese was being planned. What then? There don't know when, or how - what direction.
There is still scope for 'cock-ups', they can't go on alerts continuously! Presumably there will be recon flights, submarine patrols
OTOH IMHO they don't want to arose any suspicion that they 'know', but they need to be able to give the Japanes a warm welcome when they do arrive, though the Zero will still be a surprise.
What's next?

Military radio traffic would spike around Oahu. Unless a Midway style mess up in transferring intel occurred, Nagumo would be made aware that the hornet's nest was buzzing and would probably follow his orders to abort the attack if discovered prior to 24 hours beforehand.

 

[Peg Leg Pom]

You know what Mr President I don't think we should leave the Pacific Fleet at Pearl Harbour. We really should keep most of it in San Diego where it belongs.

 

[alspug]

As bad as Pearl Harbour was the issue with any more then 3 or 4 hours warning is that the Battleships are not recoverable and the losses would be far worse. The IJN Pilots where literally the best in the world at the time when it came to Anti-Shipping attacks. The US Navy at the time was overconfident as was the RN as well. The Americans given even a weeks warning would throw out some Submarines as a trip wire and attempt to use the Carriers to soften up the IJN for the Battleships. End result would be US Carriers and Battleships sunk. The aircrew losses in Pearl Harbour and follow up operations along with the Soft and Risk adverse use of the USN Carriers after Peal Harbour gave the Americans time to learn and digest some hard to swallow pills.

The US Navy was rapidly improving in the leadup to Pearl Harbour but was around 3 months from having all the pieces in place not including experience to attempt to fight carrier to carrier. By Midway the USN had absorbed the lessons from multiple battles, carrier raids and a full fleet engagement and still came close to ruin. The IJN on the other hand had an incredible force that got weaker over time due to the nature of the pilot training program.

 

[Draconis]

Military radio traffic would spike around Oahu. Unless a Midway style mess up in transferring intel occurred, Nagumo would be made aware that the hornet's nest was buzzing and would probably follow his orders to abort the attack if discovered prior to 24 hours beforehand.

And then what happens? The Japanese will still carry out all the other attacks that were scheduled to begin about the same time. The landings in Malaya, the DEI and the Philippines. What will they do with their Kido Butai? Would fuel concerns send then directly back home or will they hit Wake or Midway on the way?

 

[Gillan1220]

And then what happens? The Japanese will still carry out all the other attacks that were scheduled to begin about the same time. The landings in Malaya, the DEI and the Philippines. What will they do with their Kido Butai? Would fuel concerns send then directly back home or will they hit Wake or Midway on the way?

The KB would probably redirect its attack on the Philippines, which was the greatest obstacle to the Japanese conquest of Asia.

 

[Glenn239]

And then what happens? The Japanese will still carry out all the other attacks that were scheduled to begin about the same time. The landings in Malaya, the DEI and the Philippines. What will they do with their Kido Butai? Would fuel concerns send then directly back home or will they hit Wake or Midway on the way?

That's an interesting question. On the logistics front, some background off the top of my head, (ie, not double-checked). For Pearl Harbor, Kido Butai had 8 tankers allocated, (1 might have not been available though, would have to double-check). That translates into at least 70,000 tons of refuelling oil. Capacity for KB (6 carriers, 2 battleships, 3 cruisers, about 11 destroyers) might have about 60,000 tons, plus some provisions for extra storage. This gave a range of 7,500nm at 18kt, or 8 tons per mile. (cruising speeds were more economical than 18kt, so 8 tons per mile might be overstated).

If the attack is aborted prior to the 24 hour mark then the final high speed run to target will not be made. At that point, Nagumo has travelled maybe 2,700nm and has consumed over 20,000 tons of fuel, leaving something about 50,000 tons with his tankers, plus the 60,000 tons aboard his ships, (which had been for many top upped on the way). Nagumo has the tanker capacity to undertake an alternate mission. (The 48 hours of the 24kt high speed run would have consumed more fuel than the cruise from Japan to the point north of Oahu where it commenced, so the fact that Nagumo has aborted before the high speed run starts has a large impact on his logistics).

Midway is close by to his approach route, but there are some disadvantages. First, the weather was unpredictable to the north of MIdway, (and indeed, turned poor on the return journey). Second, the fact that Oahu had been altered and the US carriers were unaccounted for might cause some concern aboard Akagi that there was a danger of facing a counterattack by the main weight of the US fleet. Third, (and probably most importantly), Nagumo's command had undertaken plenty of intensive specialist training, but none of it involved long range recce - the precise skill that would be required here. (Nagumo had plenty of crews trained well enough for scouting, of course, but at this time I think that the range employed was 250nm and the chances of scouts getting lost and requiring homing signals was high).

Put that all together and my guess would be that Nagumo reverses course back along his approach route and passes Midway to the north. At that point he turns south to support Wake and then perhaps hits Midway from the southwest, (the weather south of Midway being better). I doubt Nagumo wants to return to Japan empty handed, but given 1st Air Fleets tendency to raid and bolt, I doubt a major fleet action would be improvised out of a cancellation of the surprise attack.

 

[The Laughing Hyenas]

Let's say the famous "Oh, that's nothing" radar guy calls the attack warning for an airborne attack. All the American planes would be up. MAYBE a B-17 could even catch a carrier. Certainly the presence of so many fighters over Hawaii would lessen casualties. Every ship and every AA gun would be at full alert. I could see a lot of the effects of the attack being blunted. Maybe a lot of the Japanese pilots would be lost both by lack of aircraft carrier and by American flyers with a full tank of gas going on the attack.

 

[marathag]

The IJN Pilots where literally the best in the world at the time when it came to Anti-Shipping attacks.

The same ones that had' Buck Fever' and absolutely wasted hlave a dozen torpedoes on Utah?

And nothing was moving.
Against moving target, the Kates would be wasting Ordnance dropping from 10,000 feet with the AP Bombs

 

[alspug]

The Kates would not be dropping AP bombs from 10,000feet . That was a bomb specifically modified from a Shell for that specific mission. I have not seen any evidence of it being used in any other missions. The Kate was normally a torpedo bomber and the Val's the Dive Bomber. The type 99 was a 16 inch shell modified for use as an AP bomb. 30 kg of explosive. Only carried by the Kate.
The Val carried a 250kg bomb and could not have seriously damaged the RN carriers but easily damaged the USN carriers. the USN carriers could be repaired more rapidly however the RN armored carriers could have handled a dozen Val's attack them and simply landed aircraft afterwards and carried on. The Kates on the other hand carried an excellent torpedo.

As for the wasting of torpedo's on Utah, she may have been a target ship but noone at the time was more capable. The RN pilots had more battle experience but it was spread out amongst far more pilots. The IJN had a tiny number of elite pilots and in a long war that was a terrible mistake.

 

[vizzer]

Wasn't part of the problem at PH that the fleet had only just returned to harbour after being deployed in response to warnings and now needed some time to recover.
So an earlier warning may move this sortie forward with the fleet either getting ready to set off again after returning or have actually departed again when the attack arrives.

 

[Glenn239]

Wasn't part of the problem at PH that the fleet had only just returned to harbour after being deployed in response to warnings and now needed some time to recover.
So an earlier warning may move this sortie forward with the fleet either getting ready to set off again after returning or have actually departed again when the attack arrives.

Not that I'm aware. Pennsylvania and a couple cruisers might have been in dockyard, but the fleet itself was sortie-capable.

 

[Carl Schwamberger]

The fleet had been sortied for a week, in response to the war warning messages of November. Kimmel ordered it back in to complete it's conversion to war conditions, and do some maintenance.

The Army/Navy air fleet was in rough shape after a week of maximum effort air ops. Inexperienced ground crew, no spare parts reserve, and critical tools not delivered. The deadline of the reconisance squadrons was near 50% middle of the previous week & the combat groups were in bad condition as well.

Ironically had the Japanese been able to stick to schedule & attack earlier the air defense would have been in better shape, and a larger part of the fleet off at a distance, over the horizon & time consuming to locate.

 

[Anarch King of Dipsodes]

No, I'm going back to August 1941 when Double-agent 'Popov' was interviewed by Hoover himself at the FBI. 'Popov' was sent to the US under instructions from the German Secret Service, he was meeting the FBI under the instructions of the British Double XX Committee.
A big part of Popov's brief was to get information on Pearl Harbor defences - for example torpedo nets - were they used, when etc. He had information on the Japanese interest in the British RN attack on Taranto - the Japanese visited the base.

The text of the "shopping list" of questions given to Popov (his real name; his British code name was TRICYCLE) is public. It was published in The Double-Cross System in the War of 1939-45 by J. C. Masterman, which was the official report to the British government composed at the end of the war.

Only part of the list is questions about US facilities in Oahu. Those questions cover a wide range of military and related facilities in Oahu. None of the questions - I repeat: none - would apply to Japanese plans for an attack by carrier planes on the anchored battle fleet.

Wait - that's not quite true. One question is

"Number of anchorages?"

which is applicable, though extremely general.

One third of the list is questions about "ammunition dumps and mine depots" on land. Another third is questions about airfields. The remaining third is about Pearl Harbor, but it includes questions about drydocks, the submarine station, the minelayer/minesweeper base, and a "floating dock". A question about torpedo nets clearly applies to nets deployed by ships at sea, not harbor defenses.

Since Oahu hosted numerous important US military and naval facilities which would be used in a war with Japan, of course Japanese intelligence was interested - regardless of any thoughts of attacking the US fleet in Pearl Harbor.

As of August 1941, not only had the Japanese high command not decided on any such attack, the necessary equipment and tactics had not been developed. Air-dropped torpedoes could not be used in Pearl Harbor because the dropped torpedoes would initially plunge to bury themselves in the shallow bottom there. The Japanese Navy overcame this difficulty by fitting the torpedoes with wooden "wings" extending to each side. The "wings" checked the fall of the torpedo at the water surface and broke off. Development and testing of this new technique was not completed until October 1941.

 

[Carl Schwamberger]

....

As of August 1941, not only had the Japanese high command not decided on any such attack, the necessary equipment and tactics had not been developed. Air-dropped torpedoes could not be used in Pearl Harbor because the dropped torpedoes would initially plunge to bury themselves in the shallow bottom there. The Japanese Navy overcame this difficulty by fitting the torpedoes with wooden "wings" extending to each side. The "wings" checked the fall of the torpedo at the water surface and broke off. Development and testing of this new technique was not completed until October 1941.

This is something the conspiracy theorists overlook. Japans decision for war came much later. The debate within the government ran on for months, and was not taken in ernest until the negotiations broke down September-October.

Beyond all that the US Navy never dismissed the idea Oahu would be attacked. The difference was in the form of attack. In the USN view submarines lying in ambush off Hawaii were a given, as were surface raiders like cruisers operating at a distance. Several times in the 1920s & 1930s the USN tested the idea of a carrier raid on Hawaii & Panama & judged it practical. The surprise was in the scale of the raid - the number of carriers, and the direction, & of course the exact date. The War Warning messages were off by a week.

 

[Carl Schwamberger]

The text of the "shopping list" of questions given to Popov (his real name; his British code name was TRICYCLE) is public. It was published in The Double-Cross System in the War of 1939-45 by J. C. Masterman, which was the official report to the British government composed at the end of the war.

Only part of the list is questions about US facilities in Oahu. Those questions cover a wide range of military and related facilities in Oahu. None of the questions - I repeat: none - would apply to Japanese plans for an attack by carrier planes on the anchored battle fleet.

Wait - that's not quite true. One question is

"Number of anchorages?"

which is applicable, though extremely general.

One third of the list is questions about "ammunition dumps and mine depots" on land. Another third is questions about airfields. The remaining third is about Pearl Harbor, but it includes questions about drydocks, the submarine station, the minelayer/minesweeper base, and a "floating dock". A question about torpedo nets clearly applies to nets deployed by ships at sea, not harbor defenses.

Since Oahu hosted numerous important US military and naval facilities which would be used in a war with Japan, of course Japanese intelligence was interested - regardless of any thoughts of attacking the US fleet in Pearl Harbor. ...

Exactly. These are questions I would ask even if not attacking Pearl Harbor. Its all useful information for understanding Oahu as a fleet base, which bears directly o US offensive ability. When this list was written the fleet had bee relocated to Oahu less than a year & naturally the Japanese wanted t understandings its utility as a base of operations.

 

[Anarch King of Dipsodes]

The War Warning messages were off by a week.

Indeed. Not long ago, a poster here noted that after the "war warning" was issued, "the brass went crazy" (in the words of a veteran who had been there). Continual alerts, extra patrols, even moving the fleet to sea. But after a week of nothing happening, "the brass" decided to stand down over the weekend and let the forces get some rest, catch up on deferred maintenance of aircraft, resume training operations, and so on.

If the "war warning" had been delayed by three days...

 

[Carl Schwamberger]

Or if the reaction had been a bit more 'measured'.

 

[MUC]

Let's say the famous "Oh, that's nothing" radar guy calls the attack warning for an airborne attack.

That would give the American forces only a short warning. Detection occured at 7:02, the report was dismissed / interpreted as B-17s at 7:20, the first wave reached Oahu at 7:40, attack formally began at 7:55.
So, if the report of the radar site was classified as an inbound raid at 7:20 (let‘s even say 7:15 for the sake of the argument), what would happen next? A pair of P-40§ are sent out to investigate?

All the American planes would be up.

Certainly, not all. Some, yes.

MAYBE a B-17 could even catch a carrier.

I highly doubt that.

Certainly the presence of so many fighters over Hawaii would lessen casualties. Every ship and every AA gun would be at full alert. I could see a lot of the effects of the attack being blunted. Maybe a lot of the Japanese pilots would be lost both by lack of aircraft carrier and by American flyers with a full tank of gas going on the attack.

Yes, the Japanese would suffer higher losses.