Rn vs IJN

[Wild_Bill_Kelso]

Hi
As has been noted it is very hard to get Britain and Japan fighting each other without the actions of the USA taken against Japan over China, indeed the Anglo-Japan agreements may have lasted longer. However, all that can be done is guess what could have happened from the activities of both navies in various situations or actual incidents between the navies.
One incident from 16th May 1945 was the sinking of the Japanese cruiser 'HAGURO' in a night battle with RN destroyers. The armament of the former at the time appears to have been 10 - 8 inch (5x2), 8 - 5 inch DP (4x2) and probably 8 - 21 inch torpedoes (2x4) plus AA. Details of this night action follow:
First from the OH 'The War Against Japan Volume V':
View attachment 732409
Second from OH 'The War at Sea 1939-1945 Volume III, Part II':
View attachment 732410
Third from 'Radar at Sea' by Howse, giving details of radar use in the lead up to the battle:
View attachment 732412
View attachment 732413
I hope the example is of use.

Mike

Great story with a lot of interesting details. I love how the radar plotter was called the "schoolmaster"

 

[Wild_Bill_Kelso]

It's very difficult to ponder this scenario in isolation from events in Europe, but even in the best case scenario for RN (no war in Europe), many of the weaknesses in the RN will still apply.

By far imo is the carrier force, not only the RN CVs carry less aircraft than KB, but the aircraft themselves are still the likes of Fulmar, Albacore, maybe Sea Hurricanes and some Seafires at best, Skuas, Swordfish. As i understand their combat radius is much shorter than KBs, so in a fight the KB could just stay 250 miles out and keep sending strikes at the british force, with little to fear in the way of retaliation. Not only that but Fulmar and Hurricanes proved completely outmatched by the Zero in 1942, and the Spitfire got roughly handled by the same too in 1943. I can't see the british putting 100 strike aircraft over KB within 1 hour like the USN did at Midway, to overwhelm it's defences.

So imo, as far as a 1942 stright carrier fight, all things being equal the RN will be eaten alive, and KB will cover itself in glory. There is the issue of the supposed carrier night-fighting superiority of the british, but this assumes a lot of things, first the IJN will be kind enough not to attack during the day, let itself be tracked, then be kind to stay within 150 miles or whatever the Albacore's combat radius is. That's a lot of ifs, and any british night strikes, not to mention significant damage, would be more of a fluke rathern than something to be expected.

Even fast forward to 1944, you will have at best Barracudas, Fireflies, Seafires (i'm ignoring for the moment the US planes, afterall the UK would not seem/feel into a tight spot to ask the US for help yet since it's only fighting Japan in this scenario - in fact they will be thinking humiliating to do so) against the B6N, D4Y and improved Zeros. The range advantage firmly remains with IJN. And how many fleet carriers can the RN muster in 1944? I can't see them having 15 fleet carriers and 900 planes like TF58 had, even if they haven't lost a single one to date, certainy not the planes as RN carriers generally carried less aircraft compared to KB. And god forbid if IJN hasn't lost any either. To be honest, even the OTL weakened Ozawa's force, with it's undertrained aircrews, would still be a real threat against whatever carrier force the british could muster in 1944, nevermind a better trained and more numerous IJN carrier force. I can't see the british coping with 300 planes hurled at them and escape without serious damage, nor them being able to send 200 planes at 300 miles after Ozawa.

My view anyway.

I think you are right to a point, but I wouldn't discount the night attack capability of the RN with the Swordfish, and also with long range Wellingtons. The IJN and IJA were not really well positioned for night combat whereas the British were already getting used to it, and they were certainly used to hunting U-boats. They proved at Taranto that the Swordfish could be really lethal under the right circumstances.

So I think this would become clear fairly early, and IJN and RN would both try to play to their strengths. I agree IJN is in a big, big advantage in any day time carrier clash. But as other people have pointed on in this thread, weather was unpredictable and often very bad (as in rainy, cloudy, foggy) in the South Pacific, not just in the Solomons either. And the Swordfish proved capable of operating in quite bad weather (i.e. squalls). So there could be plenty of opportunities for 'bad weather' strikes. One issue would be the speed of the various fleets. Could RN stay away from the IJN fleets?

Seafires did not perform as well as Spitfires, but I think a late 1942 or 1943 vintage Spitfire such as a Mk VIII or Mk IX would indeed hold it's own against a Zero. Maybe it wouldn't dominate, since the F4Us didn't in 1943. But it would be a tough match. Tougher than a Wildcat and probably tougher than a P-40 too. Comparable probably to a P-38 at least in terms of combat. And that means that RN could protect land bases from attack, if they delivered enough of their better quality land based fighters, and control some land bases that could threaten IJN. You could put Beaufighters for daytime strikes or strafing attacks - and they seemed to do well against the IJN. Maybe Beauforts too. Wellingtons flying at night would be a more serious problem for the IJN I think.

There is a likelihood here of some surface battles of course. I give the edge to the Japanese on this, at least in the early days, but the British will start to pull ahead as they produce more modern warships and improve their radar and associated procedures.

And of course we will have the submarine war, in which the RN should pose much more of a threat to the IJN than US submarines did.

 

[Wild_Bill_Kelso]

overall I suspect it would be a similar balance to US vs IJN, in the sense that IJN would have an initial advantage which would give way gradually in an attrition war. The question would be, is the RN able to withstand IJN carrier raids in the opening year or two of such a conflict. I kind of doubt it but it would depend on the details - both in terms of technical traits and tactics.

 

[Shortround6]

A couple of departures from History that might make this more plausible, because without the US in 1942 the RN would be toast trying to fight a 3 front war.
1940,
more French ships either join the British or sail from French ports to British ones and get interned. More to free up British ships from watching them than to try to the French ships as additions.
1941.
The British stay in NA and don't get caught in Greece.
The British kick the Italians out of NA before Rommel can really set up shop.
With land based air the British beat up the Italian navy to greater extent and Italy drops out of the war (a biggy)
Fewer losses in the Med.
Fewer ships need to ride herd on the Italian navy, Send more 'stuff' to the far east.

All hypothetical to get something going.

 

[Shortround6]

And of course we will have the submarine war, in which the RN should pose much more of a threat to the IJN than US submarines did.

Yes and no.
The British have better torpedoes, but if the British subs cannot reach the patrol areas that the US subs did then it is equally pointless.
The U class was good for about 5000 miles at 10-11kts.
The S class was good for not much more until late.
Only the T class had the range to even think about operating in the Pacific. They were about 1100 ton boats and topped out at about 15kts. The US fleet boats were around 1500 tons and could make 20-21kton the surface with a bit better cruise than the T's. The British boats can do a lot of local stuff but they cannot do the merchant warfare the US boats did.

The British did have some larger interwar subs but not enough, about 24 boats but 9 of them had been sunk by the end of 1940.

 

[Wild_Bill_Kelso]

Yes and no.
The British have better torpedoes, but if the British subs cannot reach the patrol areas that the US subs did then it is equally pointless.
The U class was good for about 5000 miles at 10-11kts.
The S class was good for not much more until late.
Only the T class had the range to even think about operating in the Pacific. They were about 1100 ton boats and topped out at about 15kts. The US fleet boats were around 1500 tons and could make 20-21kton the surface with a bit better cruise than the T's. The British boats can do a lot of local stuff but they cannot do the merchant warfare the US boats did.

The British did have some larger interwar subs but not enough, about 24 boats but 9 of them had been sunk by the end of 1940.

Well I'm presuming they could operate out of Singapore, Hong Kong, or Malaya at least for a while. Or failing that Ceylon etc.

 

[Wild_Bill_Kelso]

A couple of departures from History that might make this more plausible, because without the US in 1942 the RN would be toast trying to fight a 3 front war.
1940,
more French ships either join the British or sail from French ports to British ones and get interned. More to free up British ships from watching them than to try to the French ships as additions.
1941.
The British stay in NA and don't get caught in Greece.
The British kick the Italians out of NA before Rommel can really set up shop.
With land based air the British beat up the Italian navy to greater extent and Italy drops out of the war (a biggy)
Fewer losses in the Med.
Fewer ships need to ride herd on the Italian navy, Send more 'stuff' to the far east.

All hypothetical to get something going.

For the hypothetical scenario i was assuming no war in Europe (Cold War?) or maybe a short inconclusive war (Hess treaty?)

I know any 'what if' for this situation is unhistorical by it's nature. But it's also something I suspect both the IJN and RN leadership did have to think about during the 30s as a possibility.

 

[RCAFson]

It's very difficult to ponder this scenario in isolation from events in Europe, but even in the best case scenario for RN (no war in Europe), many of the weaknesses in the RN will still apply.

By far imo is the carrier force, not only the RN CVs carry less aircraft than KB, but the aircraft themselves are still the likes of Fulmar, Albacore, maybe Sea Hurricanes and some Seafires at best, Skuas, Swordfish. As i understand their combat radius is much shorter than KBs, so in a fight the KB could just stay 250 miles out and keep sending strikes at the british force, with little to fear in the way of retaliation. Not only that but Fulmar and Hurricanes proved completely outmatched by the Zero in 1942, and the Spitfire got roughly handled by the same too in 1943. I can't see the british putting 100 strike aircraft over KB within 1 hour like the USN did at Midway, to overwhelm it's defences.

So imo, as far as a 1942 stright carrier fight, all things being equal the RN will be eaten alive, and KB will cover itself in glory. There is the issue of the supposed carrier night-fighting superiority of the british, but this assumes a lot of things, first the IJN will be kind enough not to attack during the day, let itself be tracked, then be kind to stay within 150 miles or whatever the Albacore's combat radius is. That's a lot of ifs, and any british night strikes, not to mention significant damage, would be more of a fluke rathern than something to be expected.

Even fast forward to 1944, you will have at best Barracudas, Fireflies, Seafires (i'm ignoring for the moment the US planes, afterall the UK would not seem/feel into a tight spot to ask the US for help yet since it's only fighting Japan in this scenario - in fact they will be thinking humiliating to do so) against the B6N, D4Y and improved Zeros. The range advantage firmly remains with IJN. And how many fleet carriers can the RN muster in 1944? I can't see them having 15 fleet carriers and 900 planes like TF58 had, even if they haven't lost a single one to date, certainy not the planes as RN carriers generally carried less aircraft compared to KB. And god forbid if IJN hasn't lost any either. To be honest, even the OTL weakened Ozawa's force, with it's undertrained aircrews, would still be a real threat against whatever carrier force the british could muster in 1944, nevermind a better trained and more numerous IJN carrier force. I can't see the british coping with 300 planes hurled at them and escape without serious damage, nor them being able to send 200 planes at 300 miles after Ozawa.

My view anyway.

On paper the KB should have destroyed the USN and RN carrier TFs that it encountered...but it never did. On paper the IJNs aircraft were supposedly clearly superior to the USN's mix of aircraft and yet in each encounter the KB or one its TFs never was never able to bring off a clear victory. On 4 June 1942, 3 squadrons of USN SBDs with about 45 effective aircraft, with a mix of 500lb and 1000lb bombs surprised and effectively destroyed 3 KB carriers in as many minutes. The 4th carrier was destroyed not long after. Carrier warfare wasn't decided by superior aircraft performance, rather it was about finding and hitting your opponent first.

Even Somerville, commanding the historically depleted FAA and heavily attrited RN on 5 April 1942 with his two carriers carried 45 Albacores, each capable of carrying a torpedo or up to 4 x 500lb bombs. The three Albacore squadrons were ready to go on the very late afternoon of 5 April 1942, to attack just after sunset, pending another recon report... On 9 April 10 RAF Blenheims flying at 12000ft attacked the KB (with 5 fleet carriers, and CAP aloft) and bombed it's flagship, with complete surprise; imagine if that was two or 3 squadrons of Skuas. Historically the FAA was perpetually fighting with a shortage of aircraft and aircrew but that won't be the case with no war in the ETO/MTO.

Let's give Somerville 5 fleet carriers (and a couple dozen submarines) and 4 or 5 shore based FAA/Coastal Command strike and recon squadrons on Ceylon, and add in a fully functional radar GCI system on Ceylon with another couple of RAF/FAA fighter squadrons and refight that encounter. RN carriers operated with small deck parks when the aircraft were available and Somerville's 5 fleet carriers would have aid from 150 shore based aircraft plus ~250 aircraft onboard vs 275 for the KB.

Historically the USN's subs were fitted with nearly useless torpedoes but in this scenario a massively expanded RN submarine force is going to devastate Japanese shipping from day one.

The BEC had nearly 3 times Japan's steel production and a far larger aircraft industry and a far more productive ship building capacity. The RN could have easily laid down a dozen light fleet carriers, for example, in 1940 or 1941 or even early 1942 and had them ready by mid 1944.

 

[RCAFson]

Yes and no.
The British have better torpedoes, but if the British subs cannot reach the patrol areas that the US subs did then it is equally pointless.
The U class was good for about 5000 miles at 10-11kts.
The S class was good for not much more until late.
Only the T class had the range to even think about operating in the Pacific. They were about 1100 ton boats and topped out at about 15kts. The US fleet boats were around 1500 tons and could make 20-21kton the surface with a bit better cruise than the T's. The British boats can do a lot of local stuff but they cannot do the merchant warfare the US boats did.

The British did have some larger interwar subs but not enough, about 24 boats but 9 of them had been sunk by the end of 1940.

It required very little in the way of modification to increase the S and T class ranges to 8000 and 11000nm respectively; basically just converting some ballast tanks to fuel tanks. It wasn't until 1943/44 that the RN contemplated doing so because their subs were fully committed in the ETO/MTO until then. Historical RN sub production was bottlenecked by the need to build convoy escorts. Anyways, trying to create a scenario where the RN has to fight a '3 ocean war' with it's historical forces isn't going to work unless things are far different in the ETO/MTO.

The transit cruise speeds of all subs were on the order of 10 knots. It was only for relatively short periods of time that subs would 'sprint' whilst on the surface.

 

[Wild_Bill_Kelso]

On paper the KB should have destroyed the USN and RN carrier TFs that it encountered...but it never did. On paper the IJNs aircraft were supposedly clearly superior to the USN's mix of aircraft and yet in each encounter the KB or one its TFs never was never able to bring off a clear victory. On 4 June 1942, 3 squadrons of USN SBDs with about 45 effective aircraft, with a mix of 500lb and 1000lb bombs surprised and effectively destroyed 3 KB carriers in as many minutes. The 4th carrier was destroyed not long after. Carrier warfare wasn't decided by superior aircraft performance, rather it was about finding and hitting your opponent first.

Woah nelly. You kinda rushed through this bit right here. USN was close to parity against the IJN in terms of carrier aircraft. FAA was not. That's just a fact.

FAA had zero success against the zero. And didn't have any British fighter that could hold it's own. FAA strike aircraft were a generation behind the Japanese aircraft. The D3A was arguably the best dive bomber in the world. Certainly it was in the top 3. The same cannot be said for the Skua, Swordfish, or Albacore.

Even Somerville, commanding the historically depleted FAA and heavily attrited RN on 5 April 1942 with his two carriers carried 43 Albacores, each capable of carrying a torpedo or up to 4 x 500lb bombs. The three Albacore squadrons were ready to go on the very late afternoon of 5 April 1942, to attack just after sunset, pending another recon report... On 9 April 10 RAF Blenheims flying at 12000ft attacked the KB (with 5 fleet carriers, and CAP aloft) and bombed it's flagship, with complete surprise; imagine if that was two or 3 squadrons of Skuas. Historically the FAA was perpetually fighting with a shortage of aircraft and aircrew but that won't be the case with no war in the ETO/MTO.

Uh, it's amazing that you even bring this up to brag about. The Blenheims got lucky enough to try to bomb the Japanese ships but missed with every bomb and lost four aircraft, which you neglected to mention, claiming one zero with defensive fire.

Let's give Somerville 5 fleet carriers (and a couple dozen submarines) and 4 or 5 shore based FAA/Coastal Command strike and recon squadrons on Ceylon, and add in a fully functional radar GCI system on Ceylon with another couple of RAF/FAA fighter squadrons and refight that encounter. RN carriers operated with small deck parks when the aircraft were available and Somerville's 5 fleet carriers would have aid from 150 shore based aircraft plus ~250 aircraft onboard vs 275 for the KB.

They actually had over 100 aircraft in and around Ceylon (including 38 servicable Hurricanes and about 20 Fulmars) and had very little to show for them. They lost 40 aircraft, the carrier, and seven other ships. The Japanese lost 20 aircraft, almost all to AAA.

Historically the USN's subs were fitted with nearly useless torpedoes but in this scenario a massively expanded RN submarine force is going to devastate Japanese shipping from day one.

You might be overstating this a little bit.

The BEC had nearly 3 times Japan's steel production and a far larger aircraft industry and a far more productive ship building capacity. The RN could have easily laid down a dozen light fleet carriers, for example, in 1940 or 1941 or even early 1942 and had them ready by mid 1944.

By that time they would probably have been fully banished from the Pacific and may have lost significant assets in the Indian Ocean. Or worse, India itself.

 

[Shortround6]

There is more to submarine patrols than just fuel.

The American subs were deigned for a patrol of 75 days.
They carried enough food for 75 days, they had more refrigeration so fresh food lasted longer even if not the full time. They carried more water and/or had a larger distillation capacity.
The American boats were air conditioned and the air conditioning took a lot of moisture out of the air. Which not only made things more comfortable but increased reliability due to less corrosion in the electrical gear.
They also carried 24 torpedoes which meant, once they got torpedoes that mostly worked, they could engage more targets per patrol.

The U's carried 8 torpedoes or 10 if they had the two extra external tubes.
The S's carried 12 torpedoes or 13 with the single stern tube
The T's carried between 14-17 depending on the torpedo tube fit. But 2-4 tubes were outside and could not be reloaded. The external torpedoes also suffered a loss in reliability on long patrols.

You need more British boats to keep the same number of subs on station per day and with trips taking several weeks each way the number needed can go up rather quickly.

British boats could do a better job of defending Singapore, Malaya, New Guinea in the beginning but if you loose Singapore as a base the ability to interrupt the Japanese supply lines are greatly diminished.
On the plus side the rather crappy Japanese ASW would be even worse against the smaller British boats. They are smaller targets, both for weapons and for sonar, they turn better, and they probably dive faster at any given period during the war.

 

[RCAFson]

There is more to submarine patrols than just fuel.

The American subs were deigned for a patrol of 75 days.
They carried enough food for 75 days, they had more refrigeration so fresh food lasted longer even if not the full time. They carried more water and/or had a larger distillation capacity.
The American boats were air conditioned and the air conditioning took a lot of moisture out of the air. Which not only made things more comfortable but increased reliability due to less corrosion in the electrical gear.
They also carried 24 torpedoes which meant, once they got torpedoes that mostly worked, they could engage more targets per patrol.

The U's carried 8 torpedoes or 10 if they had the two extra external tubes.
The S's carried 12 torpedoes or 13 with the single stern tube
The T's carried between 14-17 depending on the torpedo tube fit. But 2-4 tubes were outside and could not be reloaded. The external torpedoes also suffered a loss in reliability on long patrols.

You need more British boats to keep the same number of subs on station per day and with trips taking several weeks each way the number needed can go up rather quickly.

British boats could do a better job of defending Singapore, Malaya, New Guinea in the beginning but if you loose Singapore as a base the ability to interrupt the Japanese supply lines are greatly diminished.
On the plus side the rather crappy Japanese ASW would be even worse against the smaller British boats. They are smaller targets, both for weapons and for sonar, they turn better, and they probably dive faster at any given period during the war.

RN subs were fitted with dehumidifiers and later effective AC as well, and the S class could do ~40 day patrols whilst the T class could do ~50 days. The USN subs were able to achieve 75 day patrols by refuelling and reprovisioning enroute, mainly at Midway. Singapore isn't going to fall in a day and in the meantime RN subs are free to operate in IJN home waters easily.

Remember that USS Tinosa proved that USN torpedoes didn't work that well on 24 July 1943 or 19 months into the war. 24 USN torpedoes were equivalent to ~5-7 RN torpedoes.

"24 Jul 1943
USS Tinosa (Lt.Cdr. L.R. Daspit) torpedoed and damaged the Japanese oiler Tonan Maru No.3 (19210 GRT) west of Truk in position 06°56'N, 147°52'E.

Tinosa fired no fewer than 15 torpedoes, of which 10 hit but only two exploded ! 8 were duds....the ship was heavily damaged but limped into Truk. It illustrated the unreliability of the American torpedoes, and efforts were redoubled to fix the faulty exploder mechanism after the Tinosa captain filed his report on the incident. He could see the Japanese crew running around the decks pointing at the torpedoes before they hit, but a loud thud was the only result time after time."
Tinosa (SS-283) of the US Navy - American Submarine of the Gato class - Allied Warships of WWII - uboat.net

Also note the number of days for Tinosa patrols.

 

[Wild_Bill_Kelso]

Man I hope you work in PR mate, you are a master of spin.

 

[Shortround6]

RN subs were fitted with dehumidifiers and later effective AC as well, and the S class could do ~40 day patrols whilst the T class could do ~50 days. The USN subs were able to achieve 75 day patrols by refuelling and reprovisioning enroute, mainly at Midway. Singapore isn't going to fall in a day and in the meantime RN subs are free to operate in IJN home waters easily.

Given enough time the British could have built bigger subs, they were working on the slightly larger A class from 1941 on with more power, better accommodations, more fuel and a few more torpedoes. Actual construction was delayed while more S and T types were built.

The British did an amazing job of fitting new equipment into the old hulls without extensive redesign (like adding 10ft or something).

The British built subs for the war they fighting in Europe and they found that the T's were to big for Med. The US boats might as well have towed a buoy behind them with a flashing light. The clearer water of the Med made spotting of subs by aircraft at at shallow depth easier than anywhere else. I believe the British even pulled some of the S boats out of the Med when they had enough U's. ?

The point is that they boats had different strengths and weaknesses. Just thinking that the British boats with their torpedoes would have given much better results that the American boats is too simplistic.
The British boats could have done a lot of good work but they needed to be handled differently.

The British were developing their boats almost continuously and while a late 1941 boat was different than a 1938 boat a 1944 boat was also different than a 1941 boat.
The British changed form riveted hulls to welded, which allowed for the use of the ballast tanks for fuel to be brought back, the riveted construction allowed too much leakage.
The welding was stronger and allowed deeper diving and stood up better to depth charging. Additions to radar and sonar and new radios was also done within existing space, no small trick on a small submarine.

The changes in habitability was actually rather marked. The early boats needed two crews and sometimes 3 crews to rotate in patrols. the later boats with air conditioning and better food and the like greatly reduced the need for extra crews ( Selected papers on British warship design in World War II )
It might also help to look at the maps while figuring out what the British ships could and could not do. It is almost 2500 N miles from Singapore to the Bungo channel. so just over 10 10 days at 10 knots without ever having to submerge. And 10 days back home. You can do it, you just can't stay for very long. At least not in 1941-42.


Figure what the British can do and not try to just plug British ships and equipment into US tactics/strategy.


The British had up to 15 submarines at Singapore in 1939. Most were gone by 1941. A few as 4 boats were operating out of Trincomalee for much of 1942 and 1943 until the Italian surrender. To heck with the Japanese home waters. 15 Subs operating in South East Asian waters in late 1941 and another 6-8 operating out of Darwin could have really screwed up the Japanese invasion plans.

 

[Wild_Bill_Kelso]

The Japanese had submarine aircraft carriers. Which they actually used a bit. Late in the war they had one which actually had good bombers.

Submarine aircraft carriers of Japan - Wikipedia

en.wikipedia.org

I-400-class submarine - Wikipedia

en.wikipedia.org

 

[Thumpalumpacus]

Comparable probably to a P-38 at least in terms of combat. And that means that RN could protect land bases from attack, if they delivered enough of their better quality land based fighters, and control some land bases that could threaten IJN.

I want an armored-deck carrier with 40 P-38s.

I'd settle for getting rid of those goddamned two-seat fighters and getting a real gunner into the brew -- one pilot, 8 guns and a *little* more than 230 kts. Skip the biplane TBs while we're at it. 1917 called, it wants its planform back.

In a surface action the RN has a solid opportunity, but in the flattop business, armored decks don't stop Type 91 torpedoes. Radar gunnery and British steel in 1941 though? Don't bet against it. Hood, Renown, and Repulse to lasso 'em in, QEs and Rs to learn 'em.

But boy, get to the flattops ... 'nother story altogether.

 

[ThomasP]

Much as I like what ifs, this discussion is somewhat silly without reasonably defined parameters.

As has been pointed out, in the historical timeline the UK would have no chance vs Japan due to the war in the ETO/MTO.

If there is no war in Europe, when does the UK begin preparing for war in the Far East? What would the differences in the OOB become vs the historical reality?

Without the distraction of the war in Europe, the UK could/would move massive amounts of manpower and material to the PTO. Singapore could/would be focused on and finished (hopefully properly). What would the response be by Japan to these movements. (Remember, the US and UK only faced about 10% of the Japanese Imperial Army forces during the war. How much of the rest of the IJA could/would be deployed?)

Are we assuming the war with Japan begins on 7 December 1941?

The UK would fight the war in the Far East war on its own terms (when possible) whatever those terms would have been. Comparing the UK chances using methods similar to those used by the US in the historical timeline is spurious, as the UK did not ever (as far as I can tell) plan on fighting a war in the Far East in a similar manner to what the US planned/did. As far as I have been able to find, the UK planned on the use of ocean choke points/zones of control/exclusion based on joint land based air forces and naval forces, utilizing large scale ground warfare as the decisive factor. It was assumed that the UK would win a war of attrition with Japan, the ultimate goal being retention of her colonies and overseas assets/investments. British intelligence was aware of the Japanese fleet strengths and weaknesses in general.

And last but not least, if Japan does not go to war with the US on 7 December 1941, are we saying that there is no war between the US and Japan (at least initially)? Or are we saying that Japan does go to war with the US and succeeds in taking out the US carriers in the early strikes/battles, with the consequences of the US requiring considerable time to regroup/recover and Japan being able to focus on the UK (at least initially)?

 

[EwenS]

Well as we seem to be talking a "what if" in 1942 without a war in Europe a few things to consider.

Theatre of operations
Inter-war the RN was not intending to fight in the Pacific with its great distances. Most from the USA do not seem to appreciate that, considering all waters east of Singapore as the "Pacific". San Francisco to PH = 2,400 miles. PH to Manila = 4,800 miles.

The intention was to fight in the South China Sea and waters south of Japan, based on Hong Kong & Singapore. Singapore to Hong Kong = 2,000 miles. It is then only another 450 miles or so from Hong Kong to Formosa/Taiwan, the nearest major piece of Japanese real estate. It is then another 800 miles or so to Kyushu and Japan proper via the East China Sea.

FAA aircraft
Remember the RN only got back full control of the FAA in May 1939.

OTL the Barracuda was seriously delayed by a number of factors caused by war in Europe. We don't know how an original in-line, air cooled Exe engined Barracuda delivered on schedule would have performed. War in Europe caused cancellation of that engine, low priority for materials, work stoppages etc. Accepted that still leaves the handling issues and Fairey's internal problems. But without the pressures of wartime? In 1939 production was planned for April 1941-April 1942. Development of a successor would have started around 1940/41 and there are some signs of this happening.

Fighters.
Again this is an unknown without the effects of war in Europe. Delays to Firefly & Firebrand. But 1942 service entry was originally envisaged. Too early for the 1942 scenario. The Fulmar was acquired as "an interim fighter" and in 1939 production was scheduled to cease in March 1941, although options were examined in 1939 to extend it if need be and to keep Fairey factories busy until Firefly was ready for production. The RN sought Spitfires in 1939 but was told no. Supermarine were working on a folding wing for it at that point. The RAF were already looking forward to the next generation in Typhoon/Tornado. So a folding wing Seafire, with a Griffon engine, is a possibility by 1942. And that would mean no Firebrand.

Carriers
No war in Europe means less interference with the pre-war building plans. So potentially:

Illustrious, Formidable & Victorious in 1940
Indomitable & Implacable in 1941 (still with that big forward lift)
Indefatigable June 1942

1, possibly more, further carrier(s) were planned for the 1940 Programme as a modified Implacable design, and more in 1941. But the Programmes were never finalised due to war in Europe. Completion from mid-1943? But the yards were pretty busy even without war in Europe, so what is realistic?

Submarines
As touched on above, inter-war the RN maintained the 4th Sub Flotilla based on depot ship Medway at Hong Kong and at Singapore, simply to target any Japanese aggression. In Sept 1939 this had 18 O/P/R class patrol subs plus 2 Rorqual class minelayers. These had been built from mid-1920s to mid-1930s.

The T class boats with their initial 10 TT (6 internal, 4 external) were the true successors to the O/P/R patrol subs. 16 were already built or building before the outbreak of war with it being the principal type going forward. The A class only came about after the disasterous 1942 Far East campaigns, when it was realised more range was required. 1943 design with first boat, Amphion, laid down in Nov 1943 and completed March 1945.

The 4th sub flotilla effectively ceased to exist after war with Italy broke out in June 1940 as its remaining boats were withdrawn to fight there, where losses were heavy, or in home waters. There were no submarines east of Suez on 7 Dec 1941. By April 1942 2 T boats were en route Med to Ceylon.

Without war in Europe the O/P/R boats would have been withdrawn and replaced by T boats over time.

Without war in Europe there would have been no S class beyond the 12 ordered and built 1930-38. The third group was begun under the 1939 War Programme and ordered from Jan 1940 as a means of maximising sub production. As for the U class, similar story. After the first 3 boats, the next batch were under the 1939 War Programme ordered 4 Sept 1939 as a mass production vessel for use in North Sea and Med. Maybe some more for training purposes but not much more.

Capital ships
Again a completely different picture. Probably:-

1 KGV in 1940, 3 in 1941 and the last in April 1942.
2 Lions by Aug 1942
Nelson, Rodney, Hood all/some potentially under reconstruction

Destroyers
Development effectively ceased between 1939 and 1942. But the trend was upwards in size and armament, to counter the big Axis vessels of that type. By 1942 the new Battle class design was driven by War experience.

Without war in Europe in 1939 the shape of the RN and FAA is nothing like the historical end of 1941. Too much happened in that intervening period.


Edit:- the T class subs were designed for a 42 day patrol.

 

[EwenS]

The historical timeline here is:-

July 1940 - US embargo of war materials, scrap metal & high octane aviation fuel and closes the Panama Canal to Japanese ships.

Sept 1940 - Japan occupies Northern French Indochina to stop US supplies flowing to China via the port of Haiphong near Hanoi (Japanese occupation of Chinese ports had already eliminated supply through those). Under pressure from Japanese, and given the situation back home (middle of BoB, threat of invasion etc), Britain closes the Burma Road the last available route for US supplies to China. Under US pressure it reopens the Burma Road a few months later.

July 1941 - Japan occupies southern French Indochina.

26 July 1941 - USA freezes Japanese assets in the USA and embargoes the supply of all oil to Japan. About 75-80% of Japan's oil came from Californian oil wells and was largely shipped in US registered / controlled (e.g. Panama) tankers. Britain and the Dutch follow.

Previous Japanese attempts in 1941 to secure alternative sources of oil from the DEI had been rebuffed by the Dutch. IIRC they wanted about 40% of DEI production (can't locate the source for that just now).

So from the beginning of Aug 1941 the Japanese options are:-
1. Back down and lose face
2. Go to war to secure what it needs.

But for Britain it doesn't leave a lot of time, even under peacetime conditions, to carry out the necessary reinforcement of the Far East by Dec 1941.

Britain had a highly developed intelligence resource in the Far Eastern Combined Bureau. Set up in 1936 and based in Hong Kong combining personnel from all three services, but with a Naval bias due to the RN being the main weapon in any war with Japan. Heavily involved in SIGINT (radio intercept, direction finding traffic analysis etc) and with links to code breakers at the Government Code and Cypher School (Bletchley Park). For example monitored the build up in FIC. Withdrawn to Singapore before war with Japan (mid-1941 IIRC).

 

[Wild_Bill_Kelso]

Again, I don't think we have to get too "Science Fiction" about the what-if. We obviously can't do anything meaningful in terms of comparison if we start to make up theoretical new planes or move up timelines for existing planes by years and assume that the development problems they had would magically go away without a war in Europe.

It's a safe bet both the RN and IJN would have actually done wargaming and serious speculation about the possibility of their going to war in the 1930s.

All we have to do is look at a reasonable approximation of the resources that would be available if RN had to face IJN on their own. The point of this thread is to explore the relative capabilities in the real world. I think it's ok to assume that war is somehow avoided in Europe, but that the UK would also not strip away all their naval assets from Europe to deal exclusively with Japan. And that Japan itself would still have to focus largely on China.

The US would probably provide some help to the UK but was often not eager (somewhat cynically) to uphold what they saw as European colonialism in (any part of) the Pacific or anywhere else in the world (even though the US was basically doing the same thing in China and the Philippines), and there were many isolationist factions in the US. So that might be enough of reason to make it to the ballpark of plausible.

Ultimately though it doesn't have to be really plausible - it's a "What If". All we have to do is define the parameters.

So as the OP, I say, give the RN whatever they actually had. Assume some assets have to stay in the Atlantic, Med or home islands, but a lot of what is available can be sent east. Since we do have some RN plans for this we can use that as a starting point. You can also ignore RN losses to the Germans if that makes the whole thing work better.