Editing Operation Downfall (section)

===Soviet intentions===
{{Main|Proposed Soviet invasion of Hokkaido}}

[[File:Romoi-Kushiro Line.png|thumb|In a proposed invasion plan, Soviet forces were to land at the remote port of [[Rumoi, Hokkaido|Rumoi]] and occupy Hokkaido north of a line from Rumoi to [[Kushiro]]]]

Unknown to the Americans, the [[Soviet Union]] also considered invading a major Japanese island, [[Hokkaido]], by the end of August 1945,<ref name = "FP">{{cite magazine |author1-link=Sergey Radchenko |last= Radchenko|first= Sergey|date= August 5, 2015|title= Did Hiroshima Save Japan From Soviet Occupation?|url= https://foreignpolicy.com/2015/08/05/stalin_japan_hiroshima_occupation_hokkaido/|magazine= Foreign Policy|location= |publisher= |access-date= February 1, 2021}}</ref> which would have put pressure on the Allies to act sooner than November.

In the early years of World War II, the Soviets had planned on building a huge navy to catch up with the [[Western world]]. However, the [[Operation Barbarossa|German invasion of the Soviet Union]] in June 1941 forced the suspension of this plan: the Soviets had to divert most of their resources to fighting the Germans and their allies, primarily on land, throughout most of the war, leaving their navy relatively poorly equipped.<ref name = "Frank">{{cite book |last=Frank |first=Richard B. |editor-last= Hasegawa |editor-first=Tsuyoshi |title=The End of the Pacific War: Reappraisals|chapter-url= https://books.google.com/books?id=XjW49VTRhxQC&pg=PA89|publisher= Stanford University Press|date=2007 |pages=89 |chapter=Ketsu Go |isbn=978-0-80475427-9}}</ref><ref>{{cite book |title=Japanese Defence: The Search for Political Power |pages=48–60 |publisher= [[Allen & Unwin]]}}</ref>{{sfn|Allen|Polmar|1995|pp=180–185}} As a result, in [[Project Hula]] (1945), the United States transferred about 100 naval vessels out of the 180 planned to the Soviet Union in preparation for the planned Soviet entry into the war against Japan. The transferred vessels included [[amphibious assault ship]]s.

At the [[Yalta Conference]] (February 1945), the Allies had agreed that the Soviet Union would take the [[Karafuto Prefecture|southern part]] of the island of [[Sakhalin]], which Japan had [[Japanese invasion of Sakhalin|invaded]] during the 1904–1905 [[Russo-Japanese War]], and which [[Russian Empire|Russia]] had ceded in the [[Treaty of Portsmouth]] after the war (the Soviets already controlled the northern part), and the Kuril Islands, which had been assigned to Japan in the [[Treaty of Saint Petersburg (1875)|1875 Treaty of St. Petersburg]]. On the other hand, no agreement envisaged Soviet participation in the invasion of Japan itself.{{citation needed|date=July 2014}}

The Japanese had ''kamikaze'' aircraft in southern Honshu and Kyushu which would have opposed operations Olympic and Coronet. It is unknown to what extent they could have opposed Soviet landings in the far north of Japan. For comparative purposes, about 1,300 [[Allies of World War II|Western Allied]] ships deployed during the Battle of Okinawa (April–June 1945). In total, 368 ships, including 120 [[amphibious craft]], were badly damaged, and another 28, including 15 landing ships and 12 destroyers, were sunk, mostly by ''kamikazes''. The Soviets, however, had fewer than 400 ships, most of them not equipped for amphibious assault, when they declared war on Japan on August 8, 1945.<ref name="JANE">{{cite book |title=Jane's Fighting Ships of World War II |pages=180–85 |publisher= [[Random House]]}}</ref><!-- Does this include the Project Hula ships? -->

For Operation Downfall, the US military envisaged requiring more than 30 divisions for a successful invasion of the Japanese home islands. In comparison, the Soviet Union had about 11 divisions available, comparable to the 14 divisions the US estimated that it would require to invade southern Kyushu. The Soviet [[invasion of the Kuril Islands]] (August 18 – September 1, 1945) took place after Japan's capitulation on August 15. However, the Japanese forces in those islands resisted quite fiercely although some of them proved unwilling to fight after Japan's surrender on August 15. In the [[Battle of Shumshu]] (August 18–23, 1945), the Soviet Red Army had 8,821 troops that were not supported by tanks and without back-up from larger warships. The well-established Japanese garrison had 8,500 troops and fielded about 77 tanks. The battle lasted one day, with minor combat actions going on for four more after the official surrender of Japan and the garrison, during which the attacking Soviet forces lost over 516 troops and five of the 16 [[LCI(L)|landing ships]] (many of these formerly belonged to the US Navy and were later given to the Soviet Union) to Japanese [[coastal artillery]], and the Japanese lost over 256 troops. According to Soviet claims, Soviet casualties during the Battle of Shumshu totaled up to 1,567, and the Japanese suffered 1,018 casualties.<!-- Is the detailed casualty information really relevant? Also, Soviet losses typically exceeded German casualties in most battles (including Soviet victories)  -->

During World War II, the Japanese had a [[naval base]] at [[Paramushiro]] in the Kuril Islands and several bases in Hokkaido.<!-- The Imperial Japanese Navy had been mostly destroyed by then, with survivors hiding in port. --> Since Japan and the Soviet Union maintained a state of wary neutrality until the Soviet declaration of war on Japan in August 1945, Japanese observers based in Japanese-held territories in Manchuria, Korea, Sakhalin, and the Kuril Islands constantly watched the port of [[Vladivostok]] and other [[seaports]] in the Soviet Union.{{sfn|Allen|Polmar|1995|pp=115–120}}

According to [[Thomas B. Allen (author)|Thomas B. Allen]] and [[Norman Polmar]], the Soviets had carefully drawn up detailed plans for the Far East invasions, except that the landing for Hokkaido "existed in detail" only in Stalin's mind and that it was "unlikely that Stalin had interests in taking Manchuria and even taking on Hokkaido. Even if he wanted to grab as much territory in Asia as possible, he was too much focused on establishing a beachhead in Europe more so than Asia."{{sfn|Allen|Polmar|1995|pp=168–175}}