The Battle of Rehe and the 10-10 Offensive
One of the most common criticisms of Chiang Kai-shek were that he hurt the war effort by delaying the offensive into Northeast China to the symbolic date of October 10th, the national day of the Republic of China and the anniversary of the Xinhai Revolution. Unearthed archives have largely debunked that line of attack, finding that October 10th actually was the time period where most of the ROC Army had been fully mobilized. Another reason for the delay was that half a week was roughly the time it took American aerial assets to arrive in the airfields of Northern China to support ROC troops. Although the PRC had a significant air force of mostly WW2 surplus planes retired from the Soviet Air Force, the Allied forces would retain consistent aerial superiority for most of the war due to the large technological superiority of Allied (primarily American) aircraft. However, total air superiority was never achieved due to the PLA Air Force's focus on fielding primarily interceptor aircraft from small, improvised, and constantly moving air fields. American Air Force commanders likened the war to an "aerial guerilla war." A small American expeditionary force had also arrived from the Philippines (American troops did not leave Japan, fearing a possible North Japanese incursion), though the overwhelming majority of forces were ROC.
Rehe, the North Chinese city directly across the border became the first offensive target, a fact that PLA planners clearly understood. Much of the city was mountainous and dominated by the famous Qing Mountain Resorts, a series of mountain palaces and temples extensively fortified by the PRC. The ROC had significantly invested in building a large armored force due to the experience of the Sino-Japanese War, where ROC armored divisions had severely bettered Japanese armored forces. However, the mountainous terrain of the Rehe area made tank offensives very difficult, although ROC M-4 Shermans were reasonably effective when they could actually get into combat. Much to the surprise of American adjuncts, PLA forces responded to M-4 Shermans with PLA Panzerfausts - hundreds of thousands of Panzerfausts had been captured by the Soviet Union upon the surrender of Nazi Germany, and PLA armies had largely acquired them in turn. Although lacking in aerial power, numbers, and training (due to the extremely heavy militia presence), PLA forces had the advantage of being on the defensive in deeply defensible territory.
Interestingly, one major phenomenon throughout the entire war was the constant fights in Shinto shrines. In the last few years of World War II, primarily 1944 and 1945, when the Japanese "National Defense State" had significantly radicalized, the Kwangtung Army had littered the cities of occupied China and Korea with Shinto shrines. Both Koreas tore down most of the shrines as a legacy of the colonial period, but in the PRC, they were quickly used as improvised mountain redoubts.[1] Shinto Shrines were almost exclusively located in very high areas, especially mountains, and often only had one easy way of entrance, extremely steep stone stairs that would prove a death-trap for advancing Allied troops. Besides Shinto shrines, the most hotly contested areas in the offensive was the Tibetan Buddhist temple Putuo Zhongcheng, which was remarkably defensible due to its location on the mountain guarding the entrance to the inner Resort. American troops involved in the Battle of Putuo Zhongcheng quickly compared it to the Battle of Monte Cassino in Italy, where the ruins of the temple provided even better cover for the defenders, who made Allied forces pay for each foot with blood. The Battle of Rehe would eventually end in the expulsion of North Chinese forces from Rehe province, opening up the advance to Liaoning, but the cost was extremely high, with an estimated 360,000 casualties for Allied forces and 320,000 for the PLA (disproportionately taken during the disorderly retreat under heavy Allied aerial bombardment - PLA forces quickly understood to stay off the main roads).
The expulsion of PLA forces from Rehe took nearly a month, but Allied forces were confident that the rest of the war would go more quickly, since the PLA no longer had the advantage of mountainous terrain. Indeed, for a brief period of time, the armored advance of the Allied armies were rapid, with fleeing, disorganized PLA infantry were nearly encircled. However, the Allied advance quickly began slowing down once they got closer to the outskirts of Jinzhou. The swamps of Liaoning quickly proved to be very difficult to pass with tanks, and worst of all, they had been extensively mined with anti-personnel explosives. The arrival of the winter hit with a fury, as the ROC Army, disproportionately manned with soldiers from Southern China (which does not get difficult winters), was incredibly poorly prepared for the winter. ROC military doctrine and experience was also largely earned while resisting Japanese troops in the humid, hot South. As ROC soldiers simply began to freeze, small regiments made the mistake of hunting the local wildlife for furs, including what would become the dreaded Marmot. Outbreaks of bubonic plague quickly became rampant in the ROC Army, particularly shocking the Americans who associated any plague with the European Black Death. The arrival of American medics alleviated the outbreaks, though they ended up suffering the highest death rate of any subsection of the US Army in history, higher than even paratroopers in Operation Normandy or marines in Iwo Jima. Endemic plague in the ROC Army, although never exploding to pandemic levels, continually sapped both morale and manpower. Although soldiers were strictly ordered to not eat or skin marmots, extreme coldness meant that many disobeyed orders.
Another tactic that would confuse ROC troops in the swamps southwest of Jinzhou(though not American troops) was that several of Jewish deportees to China had been recruited as guerrilla spies, dressed in American combat gear (taken from the Battle of Korea). ROC troops generally were not able to distinguish between Americans and say Russian Jews. In addition, several ROC troops were actual crypto-Communists who simply grew up south of the border, while there were few crypto anti-Communists in the PLA, so they often fed information or defected. As a result of these advantages, the PRC quickly cracked almost every ROC code for the entire war, holding an overwhelming advantage in military intelligence. The war also did take on an interesting racial tone, with much of the anti-Manchu rhetoric of the Xinhai Revolution returning with a vengeance, even though most residents of "Red Manchukuo" were not Manchu. Although ROC and American officers generally kept their troops in line, a notable massacre of a Mongol village in Rehe by vengeful ROC troops was quickly seized upon by Communist officials, whose official party line quickly painted the ROC as "ethnic cleansers."
Advancing through the swamps of Liaoning, ROC troops were often easy bait for PLA soldiers, who quickly became feared for their quick winter ambushes. Allied generals advised that the Allied armies simply stop advancing in the winter and wait until the weather cleared. However, when they were told that this might take until April or May, both Presidents Chiang and Russell ordered that an attack be made immediately, fearing that a longer prolonged war might lead to Soviet intervention. Interestingly, as a show of "national unity", President Russell invited both of his opponents in the election, Senator McCarthy and General MacArthur, to meetings with the Joint Chiefs of Staff, where they did offer input. The meetings actually tended to draw Russell and MacArthur closer together, because they both grew tired of the rather eccentric outbursts of Senator McCarthy, who had apparently relapsed into his alcohol addiction due to war-induced stress. As a result, He showed up to one meeting notably drunk.
The Soviets indicated that they had no desire to intervene, but neither the USA nor the ROC trusted the USSR. The Americans in particular believed that Mao was still acting under covert orders of the USSR, not as an independent actor, while the ROC did not believe so, but they still concluded the USSR could change its mind if given enough time. Thus, the Winter Offensive was immediately approved. It was a catastrophe. Smaller Allied units were quickly surrounded and destroyed in depth, causing the Allied commanders to approve human wave assaults across the entire field, which quickly ran into deadly minefields. The supply situation completely collapsed, and endemic plague stretched American medical resources to their breaking point. Evicting PLA forces from the swamps would eventually cost Allied forces nearly 550,000 casualties (including frostbite and plague), while PLA forces lost only 70,000 men. Interestingly, the death rate of plague victims was significantly lower than the historic norm, even the norm in the Third Pandemic in the 19th century, due to the hardcore work of American medical professionals, who worked around the clock. However, plague survivors were typically in no shape to actually fight for the rest of the war. American medical personnel (after taking horrible losses) were eventually supplemented by South Japanese doctors, who were immediately dispatched after ROC troops famously breached several Rehe-based PRC biological warfare labs staffed by Imperial Japanese war criminals (they were extradited to South Japan).
This was not seen as particularly problematic by the Allied forces, since the arrival of ROC reservists and additional American reinforcements meant that the Allied armies could quickly replace their troops in a way that the PLA could not. However, the losses taken by the KMT were often the most veteran troops of the ROC, to be replaced by reservists. And although the PLA could replace fewer of its losses, PLA commanders generally let the militia units take the brunt of combat, so their units rarely degraded in the same way. In addition, the advance through the swamps were so slow and grueling, that the Americans eventually decided to open up a second front, plotting a massive amphibious assault from ROC-controlled Shandong to the PRC-controlled Liaodong peninsula, centered around Port Arthur. The idea was enthusiastically pushed by MacArthur, who argued that a quick advance through the Liaodong Peninsula could encircle and destroy the entire PLA Army. However, this strategy came at a great risk. The Soviet Union had taken over the former Japanese concession in Port Arthur proper, which meant a landing would risk war.[2] Days before the 1956 elections, Russell approved the plan, but on the sole condition that American troops steer as far as possible from Port Arthur itself, only attacking Dalian to the North.
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[1] Sort of OTL, Northeastern China is the last place outside of Japan where you can find lots of Shinto shrines. ITL, instead of being neglected, they're used as defense forts due to war.
[2] OTL, they returned control to the PRC. ITL, they don't because they're so much smaller.