Anabasis of the Northern Sea

30. Defense of Southern Karafuto

Additionally, to guard against a direct Soviet landing on Hokkaidō, a part of the 4th Tank Division, established for mainland defense in Narashino, was also placed under the command of the 5th Army. Furthermore, the mobilization of the Reserve 7th Division, which would later become the 77th Division, was gradually progressing.

On the Chishima Islands, the construction of the Kita-Chishima Fortress, centered on Paramushir Island, was underway. The establishment of Army airfields, which previously only existed at the Kitanodai Airfield on Paramushir, was rapidly progressing. Two airfields, Miyoshino (on Shumushu Island) and Uruppu (on Urup Island), had already been completed. Additionally, naval airfields constructed by the Navy on Paramushir, Matsuwa, and Tennei (on Etorofu Island) were being expanded for joint Army-Navy use.

On the other hand, although fortifications were not being constructed in Karafuto, the construction of airfields was progressing more rapidly than in the Chishima Islands. At nine locations – Shisuka, Ochiai, Nairo, Ketan, Toyohara (the capital of Karafuto Prefecture), Shotoi, Konotoro, Nayori, and Toro – airfield development was underway. Especially, the airfield at Konotoro was being constructed as a large-scale facility capable of accommodating heavy bombers. In addition to the 5th Army, there were about 5.000 personnel of the Navy's Chishima Base Force in the region.

Moreover, unlike Manchuria, Karafuto and the Chishima Islands faced the sea, allowing for support from naval vessels. The Fifth Fleet operated in this area, and an agreement known as the "Agreement Between the Land and Naval Commanders of the Northern Pacific Theater" had been concluded between Lieutenant General Kiichirō Higuchi, the commander of the 5th Army, and Vice Admiral Kiyohide Shima, the commander of the Fifth Fleet.

However, just like in Manchuria, the Army's plans for offensive operations against the Soviet Union in Karafuto and the Chishima Islands had traditionally been emphasized. Initially, the plan was to seize northern Karafuto at the onset of hostilities, followed by the occupation of vital points on the Kamchatka Peninsula and Primorsky Krai across from Karafuto. However, with the transition of the Army's plans in Manchuria to a protracted campaign, the Army's plans for operations against the Soviet Union in Karafuto and the Chishima Islands had also shifted to a protracted strategy.

Especially with the reinforcement of the Soviet Pacific Fleet, the possibility of a large-scale amphibious operation against Sakhalin and Hokkaidō became a concern. As a result, the 7th Division in Hokkaidō had to strengthen its defenses in the western part of the island. The mobilization of the Reserve 7th Division aimed to defend the lightly defended eastern part of the island.

In Karafuto as well, there was a need to guard against not only the southward advance of Soviet forces from the northern border but also the possibility of amphibious operations in the south. Therefore, the newly organized 30th Guard Unit was tasked with enhancing the defense posture in the southern region of southern Karafuto, which is Japanese territory. Including the 11th Tank Regiment led by Ikeda, the forces stationed in Karafuto were planned to be placed under the command of the Karafuto Composite Brigade.

As a new challenge emerged in Sakhalin's defense, which was the direct Soviet invasion of Hokkaidō, it was deemed impossible for the 7th Division to reinforce Karafuto if the Japanese forces there became isolated and the Soviet forces landed in Hokkaidō. Thus, currently, the defense of Karafuto was expected to be carried out solely by the forces stationed there. Therefore, the Karafuto Composite Brigade was constructing defensive positions in the northern border areas. The main force of the brigade was constructing the Mount Happō position about 11 kilometers from the border, while the 30th Guard Unit was reinforcing defenses in the Notoro Peninsula in the southern part.

Once the landing of equipment and personnel led by Ikeda's 11th Tank Regiment was completed, they were scheduled to proceed to Shisuka, the garrison town of the brigade. The Horonai Plain where Shisuka is located was the largest plain in all of Karafuto. However, it posed the difficulty of becoming a low-lying marshland of 1 to 4 meters in depth during the thawing period, making it unsuitable for tank maneuvers.

However, in this region, a road called the Central Army Road was constructed, leading from Shisuka through Keton towards the Japanese-Soviet border area. It was believed that this Central Army Road and the forested areas to its west allowed sufficient passage for the advancing Soviet forces aiming southward. On the other hand, to the west of the Central Army Road lay the Western Karafuto Mountain Range, also covered with coniferous forests. However, from Horomi Pass to the Handa border area, a width of approximately ten kilometers, there were few obstacles in the form of trees, making it also conceivable for Soviet troops to pass through.

In other words, due to geographical considerations, it was highly likely that the advancing Soviet forces would deploy their main forces in the region centered around the Central Army Road. This area was the only terrain along the Japanese-Soviet border where the passage of large units was feasible. Therefore, it could be said that the decision to deploy the 11th Tank Regiment to Shisuka was made by the Karafuto Composite Brigade.

"Nevertheless, it seems that the harbor facilities and railways are not as developed as in Manchuria."

While observing the unloading operations from the transport ships, Ikeda muttered to himself.

Though Shisuka, the destination for the 11th Tank Regiment, was also a port town, the low port capacity necessitated the transport ships carrying the regiment to dock at Ōtomari. In southern Karafuto, only Ōtomari Port and Maoka Port on the west coast could accommodate ships of 3.000 tons or more. In the event of Karafuto becoming a battlefield, it would undoubtedly pose difficulties for the swift transportation of troops and supplies using railways and vessels.

Ikeda pondered this, tightening his resolve even further in anticipation of the possible Soviet-Japanese conflict that might arise.