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NOTE: This is centered on logistical, military, technological matters, which it does touch on some political aspects. Please understand my lack of knowledge on the former topics and I'll be glad if you could share any general knowledge upon the topics at hand.
This thread is a continuum of the previous thread on the attempt to gauge what an invasion of Korea by Japan would look like and how Korea should prepare for it, if possible: https://www.alternatehistory.com/discussion/showthread.php?t=372189

The main objectives were as follows:
  • Form multiple defensive lines from where maximum attrition against the enemy can be made, along the coast or further inland;
  • Deny the enemy from utilisation or exploitation of most if not all infrastructure and personnel, civilian or military, of Korean origin;
  • Utilise asymmetrical and irregular warfare to the fullest, if the multiple defensive lines have been breached and the government capitulated;
  • Allow for immediate pushback of battlefront form Korean territory if situation allows.
In the thread, Calbear mentioned that neither defence nor guerrilla warfare after capitulation was possible:
Can't be done. Zero possibility event.
The Koreans lack the industrial strength to outproduce either opponent (which BTW, is REALLY saying something), lack the money to buy weapons, and are so badly outnumbered that they can't put troops into the field in anything close to the number necessary . A multiple pronged invasion can't be stopped with the size force possible.
I will also say that there is ZERO chance, regardless of POD, that the Korean Peninsula is able to outproduce Japan in any non ASB 1910-40s. Simply not going to happen. They may manage to reach per capital GDP parity, but that still means the Japanese have an economy five times Korea's.
A well equipped force could make the enemy bleed, but even if all the Chinese supply are troops with spears they are going to flat overrun the defenders (who will literally run out of ammunition before they run out of targets). Throw in the IJA/IJN and you have an over match that starts to resemble the 1991 Gulf War.
Asymmetrical warfare only works if the enemy lets it work.
The Heer was too busy feeding troops into the Eastern Front meatgrinder to deal with the Partisans in Yugoslavia and the "Partisans" in the USSR were simply Red Army units with limited supply. Even then all those groups managed was to discomfort the Reich. If the Red Army had been defeated, how long would the Yugoslavian resistance have survived as a cohesive force?...
Playing the low intensity card against the IJA would have been suicidal. This was an army that literally forced Chinese peasant women to toss their infants into the air so soldiers could spit them on their bayonets (documented in Nanking) and kidnapped THOUSANDS of civilian women for military brothels across Asia. They would simply have killed everyone in the village until the partisans had no one left to support them.
It is also worth remembering that every "successful" partisan campaign was supported materially by outside forces, be it the British support for the Yugoslavians, the overt Soviet support for the Vietnamese, and the CIA covert support to the Muj in Afghanistan. Eliminate that and those various movement will not disappear, but their effectiveness will drop off to nothing.

So it was quite clear that in the face of a two-front war Korea probably won't succeed in defence for a prolonged period of time. Interested in how long Korea would actually last, I PM'd Calbear on what it'd basically look like:
zeppelinair said:
So I get that if the front line ends along some sort of a OTL North-South Korea border guerrilla actions are basically impossible.
So with the assumptions made in the thread continued:
  • A Sino(Manchukuo-sized warlord state)-Japanese invasion of Korea(and most likely Russia);
  • Strong cooperation between the two militaries in invading Korea, i.e. amphibious invasions;
  • A Czechoslovakia-level developed Korea, with significant levels of industry and defence, plus a small submarine fleet;
  • Complete isolation of Korea from help for the foreseeable future when war begins;
  • In rough numbers, how long can Korea last before it has to resort to guerrilla methods? A week? A month? A few months?
This question was originally asked because from what I read here if the Czechoslovaks declared war on Germany before Anschluss Germany may have become severely hampered in its war effort; since amphibious attacks are traditionally hard to conduct I was hoping I could possibly get an optimistic answer upon the matter. :p
CalBear said:
Short version is that the Koreans are screwed six ways from Sunday. There are far too many potential invasion routes out of China and too many good potential landing possibilities to be strong everywhere.
The Japanese utter blew at amphibious tactics, but with the simply stunning number of potential landing locations available and with the overwhelming power of the IJN to take control of any area it so chooses there is no way to stop them. Extract heavy casualties maybe, but losses are not going to do anything but piss the Japanese off. Land invasion routes are numerous and virtually impossible to interdict. If the U.S./UN forces, with air supremacy at a level rarely seen, was unable to seriously interdict the PLA "volunteers" with everything from jet fighter-bombers to B-29s, the chances of a an early 1940s force of relatively modest size (which is all Korea could manage, even if it replicates the Czech industrialization) won't have a prayer. Again, possible to make the invader bleed, but against an invader that simply doesn't care.
If the main forces of the ATL Korea retained cohesion for 60 days it would be a major achievement. No serious hope of resupply of any oil/lubricants, no supply from outside of raw materials or finished goods, fighting on several different threat axes while having to continue to maintain watch on remaining potential landing areas, at least until forced completely inland, with a maximum combat forces of around 3,000,000 (any more than that and production and agriculture both simply collapse) against opponents that can put 4-7 times that many troops into the field, all of which have access to resupply and have little or no concern about munitions or other critical materials.
Gulf War 1991, except the invaders are nowhere near as likely to stop short of total victory and have a somewhat different view of the Laws of Land Warfare than 1991 NATO.
There was also a follow-up on the nature of the PLA during the Korean War, which concluded that the PLA, like the IJA, was willing to see very high casualties compared to Korea.

I underlined some parts Calbear mentioned that I thought were significant in considering the "defence plan".
To put them in bullet points:
  • Korea doesn't know where Japan will launch amphibious attacks, therefore making it hard to concentrate forces
  • Korea will most likely have zero air and naval supremacy over Japan
  • The Japanese have very strong disregard towards high casualties during both attacks or defence
  • The Koreans will have used up all its major supplies such as lubricant and fuel at very short notice
  • Japan can deploy up to 4-7 times more forces than Korea, all with plenty of resupply
Here's a few more points that I think should be mentioned in understanding the futility of the defence plan:
  1. Korea has no strategic depth; its width and length by west-east and north-south is almost similar to the Polish Corridor, and Korean forces have almost no room to devise offensive strategies.
  2. There is no national redoubt for Korea; in the scenario seen above, Korea is completely surrounded except the corridor between itself and the USSR in the northeastern tip of Korea, which itself is highly vulnerable from amphibious attacks.
  3. The Culminating point of the IJN/IJA will last much longer than the entire length of the Korean peninsula.
  4. Assume the invasion occurs around the late 1930s, with technological advances similar to OTL.
These are issues I believe are solvable with reasonable PODs. I believe it possible that Korea can defend itself against both Japan and China for more than 3 or 4 months, possibly even beyond half a year. This thought arose after finding Calbear's analogy of PLA v. USAF as unfair a comparison to IJA/IJN v. ROKAF, because as much as the Chinese may have disregarded high casualties they were also adept in camouflage and ambushing at night, something the IJA was likely not trained with.

Here are a series of WIs that I find both within the range of plausibilities and possible to solve the issues mentioned by Calbear:
(note that the point is not to try defeat the Japanese/Chinese, which is ASB, but to delay complete conquest as long as possible-)

1. WI Korea possessed a sizeable submarine and aircraft fleet​
As would be obvious, I'm not particularly an expert in aviation or naval technologies; most likely any proposals for weapons Korea *may* produce will be immediately shot down. However with my cursory inspection of various wikipages I believe mass production of fighters such as Avia B-534 or Polikarpov I-16 by Korea to be quite possible; while impossible in stopping a Japanese invasion, I believe it likely that their use would put a dent on the Japanese campaign to a certain extent. I suppose a few hundred is likely, gaging from Czechoslovakian productions. The objective of the airplanes, of course, are to hamper efforts to make significant headland along the Korean coast; emphasis would be placed in light bombers and fast interceptors.

The same goes for submarines - the numerous islands along the Korean coast can host multiple submarine bases, and with development beginning from the 1910s or even by simply buying from allies and neutral countries(i.e. the US and the Soviet Union) I think Korean submarines on par with or even superior to Japanese equivalents can be acquired; unlike the IJN, who would be in need of submarines in supporting fleet v. fleet attacks, the Koreans would find submarines to be the main part of its navy, with its role being to sink as many Japanese ships as possible - I think the Salmon class submarines from the USN armed with Mark 15 torpedoes can be seen apt for that role.

2. WI Korea planned defence against Japan since 1920​

The following diagram was made by myself with base map from a mountain ranges map of the Korean peninsula. This was made after finding out that Czechoslovakia's extensive defence line, referenced several times in AH.com to be a possible deterrent against a German invasion, began construction from 1936, only a few years before the suspected German invasion; by 1938 almost 30% was finished, showing rapid preparation on part of the Czechoslovaks.(The wikipage mentions that the full construction would be finished by the 1950s, although it's almost certain that effective construction would be finished before then.)

The question therefore is to ask how successful the Japanese invasions could have been if Korea was to prepare from 1920, immediately after the supposed independence. The map above outlines what could have been the plan to defend Korea against all possible enemies, with features such as:
  • Heavy defence, such as artillery forts and Infantry blockhouses with nearby airfields, which is outlined with an olive colour;
  • Light defence, mainly simple pillboxes and other basic defence structures, outlined with dark green;
  • Line-of-redoubt defence, structures similar to the Maginot Line, being multiple layers of military facilities, outlined with brown;
  • Extensive garrisons and fortified points around individual islands, manned with both local personnel and soldiers, outlined with light green along the coast.
  • Major cities such as Seoul and Pyongyang have been identified for reference in light blue.
(Also expect multiple railways connecting all points of defence, especially connecting the interior along multiple north-south lines; harbours would be guarded with multiple lines of underwater mines)

I am not an expert on defensive structures and don't know how much of an attack this can stop. However being aware of Japanese assaults OTL mainly comprising of light infantry with rarely any artillery support, I believe that even an amphibious assault would at best look similar to Port Arthur 30 years ago or Tsingtao during WWI, with mainly waves of light infantry assaults with close naval gun support. Coupled with the mentioned points above, I can only hope that Japan's concentrated attack on the Korean peninsula could be dampened to a certain degree.

3. WI Korea knew exactly where Japan would launch amphibious attacks​
While it is very hard to believe Korea has any informants within the Japanese government of any form, previous examples OTL show that there aren't that many* points across the Korean peninsula where amphibious assaults can be carried out:
  • Pusan, during the Japanese invasions of Korea in 1592 and 1597;
  • Asan, during the First Sino-Japanese War(mistakenly identified in the original thread as Kunsan);
  • Inchon, during the Korean War(See: Battle of Inchon);
  • Yongduk, during the Korean War(by ROK marines the day before Inchon);
  • Kunsan, during the Korean War(main diversionary effort before Inchon);
  • Haeju, during the Second World War(Japanese defence plans; also proposed during Korean War);
  • Chongjin, during the Second World War(by Soviets in part of August Storm).
Wonsan/Hungnam also deserves mention for being such a major port city complex.
One should note that the reason most of these attempts succeeded was because the areas tended to be sparsely defended, with Inchon as the best example being kept by a few thousand lightly-armed North Korean soldiers; with the heavy defence structures mentioned, it is possible to guess that amphibious attacks on any possible area may result in a stabilised front; even D-Day wasn't executed on multiple spots across a wide area, and Operation Downfall only planned to attack from southern Kyushu and Tokyo. I think it possible to conclude therefore that, even if the Korean navy mentioned above has been totally annihilated, the Japanese would most likely focus its attack on one area, at most two.

*I mean, it's not like a 100 or something.
4. WI Japan were more cautious in high casualties​
A major point Calbear makes is that the Japanese were unafraid of high casualties; since the parallel example was, however, the PLA, I think we can bring this point to question.

It is obvious from OTL that the Japanese were certainly unafraid of high levels of casualties; through the 'Banzai' mentality which appears to have re-arisen as a formal attitude towards engaging in battle by the 1920s, fuelled by propaganda originating from the First Sino-Japanese War and Russo-Japanese War, they were noted to be particularly furious as individual soldiers when at battle. The attitude that their "superior mentality" will be able to defeat the enemy has proven to be true in China, when they were against entire brigades lacking modern weapons and bereft of any training; I believe that this decades-long example, along with the initial successes in Southeast Asia, was why Japan was able to sustain a similar mentality when they were against vastly superior armies by 1944.

Then comes into question whether or not Japan would be able to maintain such an attitude towards warfare when their(TTL) first major engagement arises from the stiff resistance and superior fortifications Korea hypothetically makes; as was shown in WI No. 2, given enough time the Koreans can produce a defensive line that it can proudly call as a defensive front only comparable to the Maginot Line(leaving aside, of course, the fact that OTL Maginot didn't work :p). Is it possible that, as planes drop bombs on them, a wall of pillboxes bristling with machine guns shoot up the entirety of the beachhead, heavy artillery is falling all around and entire platoons are being wiped out, that they'll be able to maintain such a brave face? I call such an idea into question.

Further notable is that even the Japanese would be forced to take action other than pushing in more troops if assaults are continuously failing; my swift and cursory glance on casualty(dead and injured) rates on amphibious attacks showed that they can range between around 8%(Okinawa) and 70%(Port Arthur) - basically, it all depends on how it turns out. While it would be ideal for the Japanese to be able to attack at calm weather with possibly one machine gun post guarding the entire area, this would definitely not be the case when the Japanese attempt an amphibious attack along any part of the Korean peninsula, with at least a few pillboxes dotted along the coastline.

(I'm basically trying to rile people to answering extensively; please don't take any of this personally. ;) Bring on the data and I'll be happy to discuss using them.)
5. WI Korea preemtively launched an assault into said Manchukuo-esque warlord state and succeeded in capturing industrial bases​

The following map was made by /u/Upvoteanthology from my request; this gives the general sense of how I imagine the world being discussed would look like. It is possible to disregard a few major things such as:
  • Primorsk S.S.R. may or may not exist; the main outline is that the Soviet Union has stayed more or less by its OTL borders.
  • Republic of China is not the entirety of China excluding Manchuria; it's still divided amongst warlords, which may or may not have become more severe to the point of becoming separate countries TTL, thus helping Japan clash them together.
  • The Polish-Korean republic simply needs to be imagined as a hinterland area and a shared sphere of influence over China by both the USSR and Korea.
  • Japan may or may not possess southern Sakhalin; if it's a major variable, then it'll be an interesting point to discuss.
This was considered upon the question of "strategic depth" and the issue of its nonexistence within Korea; because it is essentially surrounded on all sides by hostile nations, it is possible to conclude that "preemptive defence" is necessary for Korea to viably survive as a state. The main objective of a preemptive war against the "Empire of China"(an amphibious attack against Japan would at least result in complete disaster), securing a buffer zone between a possible Chinese attack and Korea, possibly destroying the infrastructure to conduct such a war in the first place. The objectives of the war would be:
  1. Capturing the South Manchuria Railroad;
  2. Securing the cities of Dalian, Mukden, and Changchun;
  3. Leading a coordinated attack against Peking if possible.
From there it is *possible* the Japanese would come to the negotiations table, as an entire front of a planned assault has collapsed; however, it is entirely possible that the invasion of Manchuria would come to nought and simply a waste of resources as the Japanese attempt an amphibious attack anyway. The attack routes would most likely look similar to that of Japan, as they had gone through the same situation IOTL 1931 through the Mukden Incident.

5.1. AHC Korea succeeds in capturing southern Manchuria​
It is entirely possible however that the invasion fails. Although it may be assumed that they are as weak or weaker than OTL since the entire point of these series of WIs are to try defend Korea as easily as possible, it is an interesting discussion over whether Japanese divisions can serve in Manchuria to defend the territory, and if so how much, and then how successful. The necessity of this debate is left entirely to those who wish to do so.

6. WI Korea retreated into Eastern Manchuria, with neutral Soviet Union​
Referencing the map used above, it is now possible to see that Korea can retreat northwards into Manchuria and USSR territory; however, like the botched plans of Czechoslovakia and Poland upon similar matters, it is highly unlikely that such a plan succeeds, namely due to:
  • The armies most likely become caught between the Chinese and Japanese armies during the initial weeks of defence;
  • The railways leading from Korea to Manchuria are under constant danger of being captured due to being in the northeastern corner of the peninsula, which is relatively more vulnerable to amphibious attacks than other areas;
  • By the time all fronts have collapsed and "it's time to leave", the area may already be entrenched with Japanese forces ready to grind any Korean assault along the railway to a halt.

This of course does not mean there are possible scenarios where such a plan succeeds. Two main ideas come to mind - either the Koreans restructure their "defence" plan to quickly evacuating to eastern Manchuria, or they station large numbers of troops in the area before the war and use those forces to "recapture" the railway from any incoming attack, separate from the defence plans within the peninsula. Another possibility is, either along with the first or second plans, soldiers are mobilised from the area to bolster either a defensive fighting retreat, attempt recapture of the peninsula from that situation, or help defend the peninsula itself while the railway is secure and supplies can be sent southwards.

7. WI Japan/Manchukuo-esque warlord state invaded the Soviet Union along with Korea​
The main point of WI No. 7 is to see how far attacks can go when they are divided; while this is contrary to the previously-stated notion that "amphibious attacks tend to happen in one or two axes of assault", the idea is based on Japan's OTL battle strategy used during the opening days of the Pacific War, when they invaded Hong Kong, Shanghai, the Philippines, Malaysia, Indonesia, and Thailand, while launching a bombing campaign on Pearl Harbour. Furthermore since Japan has seen a development of the "Northern Route" theory in order to neutralise the Soviet Union along with Germany, plans for an attack of such nature are completely possible.

The most immediate ramification of this attack is that, since the USSR and Korea are stuck in the same hole, they would most actively seek to help each other; I can see Soviet deployments to Korea along the railway under governmental permission, and actively sending supplies along the same route. This also means however that Japan would find the railways in Eastern Manchuria much more important in this scenario, meaning the supply routes are much harder to secure; Kaema Plateau would also be completely penetrated by a Japanese invasion, therefore forcing the Koreans to abandon the idea of using the area as a guerrilla base.

However this also means that the front line most likely moves quickly beyond the Korean peninsula, and that only a few divisions would be kept there for minimal defence. My belief is that this allows an "underground Korean state" to exist, similar to the Polish Underground State which "acted in" for the destroyed Second Polish Republic or to the Yugoslav Partisans; while Korea lacks the geographical "strategic depth" these examples possess, I believe that the idea of a battlefront far from Korea is significant in that it reduces Japan's attention from the area, allowing for more ambitious operations by underground organisations and partisans.

7.1. WI Japan invaded various points in mainland China(i.e. Shanghai, Hong Kong) along with Korea and the Soviet Union​
Unlike WI No. 7.2, this WI is to deal with the assumption that the Japanese invasions are essentially led by troops "unexperienced" with real war. While I am not sure how much this affects battle effectiveness in terms of statistics, I found it intuitive that there would be a significant difference between soldiers who have physically experienced death so near and those who have not. And I also believe that experience is very significant on the command level; as was argued in the "WI WAllies conduct D-Day without North Africa", experience in battle by the officers on understanding how war should be conducted is also most likely significant.

7.2. WI Japan invaded Korea and the Soviet Union after invading mainland China​
This most likely means the Japanese are much more experienced when engaging in war against the Koreans and Soviets; the defences will be broken quicker, possibly a few weeks earlier, ensuring a quicker movement of front lines and a swifter end to the Republic of Korea. This question was raised, however, in perspective of wondering what this means in terms of guerrilla warfare, due to a quicker movement of the battlefront away from Korea: does this mean partisan operations are easier, or would they become more brutal in suppressing dissent from occupied zones?

8. WI Japan invaded Manchukuo-esque state after occupying Korea, similar to Poland during Operation Barbarossa​
Operation Barbarossa, the ultimate Nazi German plan to invade the Soviet Union, occurred almost two years after Poland was partitioned between the two countries. As with the WIs above this is to remove the Japanese battlefront as far as possible from Korea and seeing how much that would affect guerrilla operations. It strikes me that when moving into Manchuria the Japanese may possibly already be overstretched due to the relatively flat terrain of Manchuria as they go northward; how that affects the situation in Korea I am not sure.

9. WI several of these WIs are combined​
There are multiple WIs at play here, several overlapping with each other. The question then is to see how many of these WIs can be combined to produce a situation for Korea that stays within the boundaries of realism(albeit with an independent Korea that becomes quite developed) that allows the longest, if possible successful, defence of Korea.

Note: I know this all sounds all very reminiscent of a certain Gudestein right now, but bear with me. Like him, I'd like to test the furthest limit of plausibility on the matter. :eek:
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