What if IJN codes changed on May 1st, 1942

In the short run the Midway garrison is ok. In the longer haul it is far worse off than the hundreds of by passed garrisons in the Pacific. One factor is its proximity to Oahu. A introductory raid on Midway would be a final training exercise for every new carrier & squadron. Surface ships would use the Japanese for target practice, & may the Emperor help any cargo runs. The IJN bases are too far away to help.

I was thinking about the actual invasion. Even if Nimitz does not counter it with surface fleet he most probably is willing to risk every submarine in striking distance in defence of the marines. Number of boats will not be the same as in OTL (24) and torpedoes have their faults, but overall there is going to be a price in parking invasion fleet next to Midway.
 
Thanks for all the replies. First, some details regarding the historical situation of Midway defences in 1941-1942.

http://www.historynet.com/midway-islands-undaunted-defenders-may-96-world-war-ii-feature.htm

https://www.ibiblio.org/hyperwar/USMC/Midway/USMC-M-Midway-3.html

So it can be seen that a significant amount of reinforcements, especially aircraft, hurriedly arrived after May 20th in the space of a week or so, when Nimitz had solid evidence that Midway was the next IJN objective. Now Nimitz visited Midway on May 2, but as far as i can read nothing was sent until after Midway was confirmed as the next target. It appears there's some lore that postulated Nimitz knew Midway will be next even before the Coral Sea battle (hence the visit) but recent historians like J. Lundstrom refute that. I think the timeline of reinforcements looks to confirm it.

Now as Carl points out, since Midway's defence will likely be weaker than in OTL if one is to assume most if not all the reinforcements that arrived in the last week of May actually do not arrive imo assuming that even against a weaker Midway defence the IJN amphibious assault will fail is rather far fetched. It has been done to death before, especially IJN landing doctrine and fire support, and i of course do not agree with what is promoted as "consensus", but regardless of that a weaker Midway defence of course increases by that much the probability of IJN success.

There is though ambiguity even today about the real numbers of troops on Midway and the opposing numbers of japanese troops. A figure of 3500-3600 US troops is frequently quoted, though in BSCA the figure is actually stated as "over 2000" (you would think that there would be record somewhere of the exact number of US troops on the island in early June surely). As for the japanese the lowest number is quoted by SS at 2500, but frequently the japanese number is stated as 5000 troops, and as high as 5800. SS postulates that difference is made by "labour batalions", now whether there is an error and actually the labourers were EXTRA to the 5000 or so troops i'm not sure. Of course, i have tried to find info of how many men Ichiki and Ota had in their respective contingents. This source appears to say that the labour batalion (only one?) was in addition to the IJN and SNLF detachments (numbering in total) aprox 5000 troops.
http://www.ibiblio.org/hyperwar/Japan/Monos/pdfs/JM-93_MidwayOperations,May-June42/JM-93.htm

Another thing i looked over was the number of transports used in MO operation (11) embarking approx 5000 troops (there were again some labour units planned to be landed at Port Moresby, and it also appears they were extra to the over 5000 IJN/IJA troops), compared to Midway (16?). It would be very puzzling to have more transports carrying just half the number of troops compared to MO.

So, IF the number of US troops is lower at 2000 something with fewer guns and less preparations (maybe even no tanks), and IF the number of japanese troops is over 5000, then actually the requirement of 3 to 1 superiority for the attacker is almost met.

As for Kido Butai, if there is no carrier battle, considering the weaker Midway defences they probably have in total about 20 aircraft lost or written off over a couple of days of attacks. If Yorktown is not at Pearl and/or it and Saratoga are not sent to challenge the invasion force then Nagumo, having suffered only light losses, will probably be sailing for FS at the end of July, likely joined by Zuikaku - and at that time probably the US carriers are preparing to assault Midway, or they are still split, 2 or 3 in the South Pacific, 1 or 2 on the West Coast (not sure if they would keep any at Pearl given the likely nuisance raids from Midway), or of course some other possibility.

Come to think of it, getting back a bit earlier, probably operation K succeeds in this TL, what they will find at Pearl, just Yorktown recently returned from the South, or maybe no carrier/s at all if Yorktown is sent straight to the West Coast.
 
There is though ambiguity even today about the real numbers of troops on Midway and the opposing numbers of japanese troops. A figure of 3500-3600 US troops is frequently quoted, though in BSCA the figure is actually stated as "over 2000" (you would think that there would be record somewhere of the exact number of US troops on the island in early June surely). As for the japanese the lowest number is quoted by SS at 2500, but frequently the japanese number is stated as 5000 troops, and as high as 5800. SS postulates that difference is made by "labour batalions", now whether there is an error and actually the labourers were EXTRA to the 5000 or so troops i'm not sure. Of course, i have tried to find info of how many men Ichiki and Ota had in their respective contingents. This source appears to say that the labour batalion (only one?) was in addition to the IJN and SNLF detachments (numbering in total) aprox 5000 troops.
http://www.ibiblio.org/hyperwar/Japan/Monos/pdfs/JM-93_MidwayOperations,May-June42/JM-93.htm

Another thing i looked over was the number of transports used in MO operation (11) embarking approx 5000 troops (there were again some labour units planned to be landed at Port Moresby, and it also appears they were extra to the over 5000 IJN/IJA troops), compared to Midway (16?). It would be very puzzling to have more transports carrying just half the number of troops compared to MO.

So, IF the number of US troops is lower at 2000 something with fewer guns and less preparations (maybe even no tanks), and IF the number of japanese troops is over 5000, then actually the requirement of 3 to 1 superiority for the attacker is almost met.

However if one takes into account the distance travelled, local foraging opportunities, and the likelihood of when the next resupply Convoy would be able to arrive, wouldn't it make sense for the Japanese to send far more supplies to Midway than they did to Port Moresby?
 
So it can be seen that a significant amount of reinforcements, especially aircraft, hurriedly arrived after May 20th in the space of a week or so, when Nimitz had solid evidence that Midway was the next IJN objective. Now Nimitz visited Midway on May 2, but as far as i can read nothing was sent until after Midway was confirmed as the next target.

If you get a chance, double-check with sources like Combined Fleet Decoded and Black Shoe Carrier Admiral. There was a tug-of-war between Washington and Pearl Harbor whether the next target would be in the SPO or the CPO. Without SIGNET the Americans are down to traffic analysis. If the weight of signals are from/to Truk then maybe the SPO wins the debate. But if the bulk of traffic are Marianas/Home Islands that's pretty compelling evidence for the CPO, meaning Nimitz is thinking about Midway.
 
Thanks for all the replies. First, some details regarding the historical situation of Midway defences in 1941-1942.

http://www.historynet.com/midway-islands-undaunted-defenders-may-96-world-war-ii-feature.htm

https://www.ibiblio.org/hyperwar/USMC/Midway/USMC-M-Midway-3.html

So it can be seen that a significant amount of reinforcements, especially aircraft, hurriedly arrived after May 20th in the space of a week or so, when Nimitz had solid evidence that Midway was the next IJN objective. Now Nimitz visited Midway on May 2, but as far as i can read nothing was sent until after Midway was confirmed as the next target. It appears there's some lore that postulated Nimitz knew Midway will be next even before the Coral Sea battle (hence the visit) but recent historians like J. Lundstrom refute that. I think the timeline of reinforcements looks to confirm it.

Now as Carl points out, since Midway's defence will likely be weaker than in OTL if one is to assume most if not all the reinforcements that arrived in the last week of May actually do not arrive imo assuming that even against a weaker Midway defence the IJN amphibious assault will fail is rather far fetched. It has been done to death before, especially IJN landing doctrine and fire support, and i of course do not agree with what is promoted as "consensus", but regardless of that a weaker Midway defence of course increases by that much the probability of IJN success.

There is though ambiguity even today about the real numbers of troops on Midway and the opposing numbers of japanese troops. A figure of 3500-3600 US troops is frequently quoted, though in BSCA the figure is actually stated as "over 2000" (you would think that there would be record somewhere of the exact number of US troops on the island in early June surely). As for the japanese the lowest number is quoted by SS at 2500, but frequently the japanese number is stated as 5000 troops, and as high as 5800. SS postulates that difference is made by "labour batalions", now whether there is an error and actually the labourers were EXTRA to the 5000 or so troops i'm not sure. Of course, i have tried to find info of how many men Ichiki and Ota had in their respective contingents. This source appears to say that the labour batalion (only one?) was in addition to the IJN and SNLF detachments (numbering in total) aprox 5000 troops.
http://www.ibiblio.org/hyperwar/Japan/Monos/pdfs/JM-93_MidwayOperations,May-June42/JM-93.htm

Another thing i looked over was the number of transports used in MO operation (11) embarking approx 5000 troops (there were again some labour units planned to be landed at Port Moresby, and it also appears they were extra to the over 5000 IJN/IJA troops), compared to Midway (16?). It would be very puzzling to have more transports carrying just half the number of troops compared to MO.

So, IF the number of US troops is lower at 2000 something with fewer guns and less preparations (maybe even no tanks), and IF the number of japanese troops is over 5000, then actually the requirement of 3 to 1 superiority for the attacker is almost met.

As for Kido Butai, if there is no carrier battle, considering the weaker Midway defences they probably have in total about 20 aircraft lost or written off over a couple of days of attacks. If Yorktown is not at Pearl and/or it and Saratoga are not sent to challenge the invasion force then Nagumo, having suffered only light losses, will probably be sailing for FS at the end of July, likely joined by Zuikaku - and at that time probably the US carriers are preparing to assault Midway, or they are still split, 2 or 3 in the South Pacific, 1 or 2 on the West Coast (not sure if they would keep any at Pearl given the likely nuisance raids from Midway), or of course some other possibility.

Come to think of it, getting back a bit earlier, probably operation K succeeds in this TL, what they will find at Pearl, just Yorktown recently returned from the South, or maybe no carrier/s at all if Yorktown is sent straight to the West Coast.

Please note that the 3:1 advantage in infantry assumes a fairly neutral geography which wading through 1000 meters of surf @ Midway is not and so that Ratio will have to be much higher unless sufficient 'funnies' and 'amtracks' are employed to give the assautlers a mechanical advantage.
 
If you get a chance, double-check with sources like Combined Fleet Decoded and Black Shoe Carrier Admiral. There was a tug-of-war between Washington and Pearl Harbor whether the next target would be in the SPO or the CPO. Without SIGNET the Americans are down to traffic analysis. If the weight of signals are from/to Truk then maybe the SPO wins the debate. But if the bulk of traffic are Marianas/Home Islands that's pretty compelling evidence for the CPO, meaning Nimitz is thinking about Midway.

I don't have CFD but as far as BSCA is concerned at one point King believed even with the OTL intelligence on the table that an attack on Midway was a deception aimed to draw the US forces away from the South Pacific where the real offensive was expected to begin. This in addition to him initially wanting Yorktown's aircraft ashore in the SP (and have the carrier sent straight to Bremerton), and resisted recalling TF16 back to Pearl (which few weeks ago he also resisted sending it to the SP for fear of exposing the CP!). So Nimitz had a lot of convincing and arguing for his case to do.

Without the crucial OTL intelligence it seems to me they would have been in serious trouble to timely and adequately counter the forthcoming IJN offensives. I think that at the subsequent Eastern Solomon battle when they had to rely largely on radio intelligence as from what i understand they haven't managed to penetrate the new codes yet it shows what could have happened at Midway in a similar situation, intelligence placed the IJN carriers either in home waters or imminetly sailing to Truk up until the battle was joined (hence Wasp being sent to refuel and all that)! This when the US forces were fully expecting the japanese counterstrike.
 
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I don't have CFD but as far as BSCA is concerned at one point King believed even with the OTL intelligence on the table that an attack on Midway was a deception aimed to draw the US forces away from the South Pacific where the real offensive was expected to begin. This in addition to him initially wanting Yorktown's aircraft ashore in the SP (and have the carrier sent straight to Bremerton), and resisted recalling TF16 back to Pearl (which few weeks ago he also resisted sending it to the SP for fear of exposing the CP!). So Nimitz had a lot of convincing and arguing for his case to do.

That'll be Yamamoto's follow-up SPO offensive gumming up the works, because I think the elements for it were gathering at Truk?

Without the crucial OTL intelligence it seems to me they would have been in serious trouble to timely and adequately counter the forthcoming IJN offensives. I think that at the subsequent Eastern Solomon battle when they had to rely largely on radio intelligence as from what i understand they haven't managed to penetrate the new codes yet it shows what could have happened at Midway in a similar situation, intelligence placed the IJN carriers either in home waters or imminetly sailing to Truk up until the battle was joined (hence Wasp being sent to refuel and all that)! This when the US forces were fully expecting the japanese counterstrike.

That sounds correct - IIRC Fletcher had just detached Wasp for routine fuelling and would not have done that if anticipating a fleet action.
 
Please note that the 3:1 advantage in infantry assumes a fairly neutral geography which wading through 1000 meters of surf @ Midway is not and so that Ratio will have to be much higher unless sufficient 'funnies' and 'amtracks' are employed to give the assautlers a mechanical advantage.

As far as i can read on the subject, they planned to cross the surf in small rubber boats and other similar small flat bottomed vessels (i supposed it is known that the japanese were widely emplying the daihatsus at that time, right?). Besides, considering the fact that many keep putting forward this rather preposterous idea that all the troops would have hade to wade in neck deep water and all that, how did they planned to unload all those cannons, HMGs and similar material!? They certainly had a plan for that, and it was surely not by wading!
 
However if one takes into account the distance travelled, local foraging opportunities, and the likelihood of when the next resupply Convoy would be able to arrive, wouldn't it make sense for the Japanese to send far more supplies to Midway than they did to Port Moresby?

The Midway invasion convoy carried 3 months supplies for the garrison, so you're correct.
 
Is it known for certain that the troops planned to land at Port Moresby were not carrying similar amount of supplies/ammunition? Would be interesting to compare.
 
That sounds correct - IIRC Fletcher had just detached Wasp for routine fuelling and would not have done that if anticipating a fleet action.

That is correct sir...
 
If the Japanese capture Midway, the garrison will starve - that is true.

But capturing Midway also denies it as a refueling and resupply station for the US submarines, meaning they will have to base out of Hawaii or Australia, considerably shortening the patrol they can go on. Shortened patrols might also reduce the attack oppurtunities, which might mean it takes the US another few months to get their torpedo problems in order.

All of which means more oil and other supplies reaching mainland Japan as it will take the US longer to destroy the Japanese merchant navy.
 
As far as i can read on the subject, they planned to cross the surf in small rubber boats and other similar small flat bottomed vessels (i supposed it is known that the japanese were widely emplying the daihatsus at that time, right?). Besides, considering the fact that many keep putting forward this rather preposterous idea that all the troops would have hade to wade in neck deep water and all that, how did they planned to unload all those cannons, HMGs and similar material!? They certainly had a plan for that, and it was surely not by wading!

Have not read the Japanese plan, but from experience at planning that sort of thing the way I'd do it is suppress the defense enough the heavy weapons could be landed via the channel on the dock, warf, or channel banks. You can rig some sort of very shallow draft rafts to carry that across the reef, but rafts are vulnerable to surf, difficult to steer, and propel. Better to take the Daihatsu into the channel
 
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