The 'South Sakhalin Offensive Operation' was the Soviet invasion and seizure of the Japanese-controlled southern half of Sakhalin island (11/25 August 1945).

Sakhalin is the Russian name for the island known to the Japanese as Karafuto, which lies just to the north of Hokkaido, the most northerly of the Japanese home islands, across La Perouse Strait. The island is 560 miles (900 km) long and up to 60 miles (100 km) wide, with an area of 27,989 sq miles (72492 km²) and a highest point of 5,279 ft (1609 m). The island is mountainous and heavily forested, but also possesses considerable areas of swampy ground. The valleys of the Tym and Poronai rivers constitute the main corridor of land communications on the north/south axis, and it was here that the Japanese had located most of their defences, centred on the town of Koton.

The Japanese and Soviets controlled the southern and northern halves of Sakhalin respectively as a result of tIn the Treaty of Portsmouth in 1905, which ended the Russo-Japanese War (1904/05) and split control of the island along the line of 50° N. The Japanese knew their southern half of the island as the Karafuto Prefecture and the Northern District. However, it was the northern half which was the more important, for it possesses significant oil fields at Ekhabi and Okha. The Japanese had oil concessions here, and in 1940 they tried without success to persuade the Soviets to sell them the northern half of Sakhalin.

At the 'Argonaut' inter-Allied conference ay Yalta in February 1945, the Soviet leader Iosif Stalin pledged to enter the war against Japan within two or three months of the defeat of Germany. This would create another strategic front against Japan necessary and, as the Western Allies appreciated, would thereby hasten the end the Pacific War. As a result of their participation the Soviets were to regain control of southern Sakhalin and the Kurile islands group, and also receive other concessions, and it was agreed that the USA would aid the Soviet forces materially in 'Hula' to accelerate the Soviet preparations for the invasion.

On 9 August 1945, the USSR unilaterally repudiated the Soviet-Japanese Neutrality Pact of April 1941 and two days later launched the 'Manchurian Strategic Offensive Operation' (otherwise 'Avgust Buri') as a full-scale invasion of Manchuria and Manchukuo. It is worth noting that this was two days after the second US atomic bombing of Japan in the 'Centerboard' attack on Nagasaki. The Soviet offensive included the invasion of the Japanese southern half of Sakhalin island: while the primary purpose of the invasion was to clear Japanese resistance, it was also to pave the way, within 10 to 14 days, for a combined invasion of Hokkaido, the northernmost of the Japanese home islands.

The Soviet invasion came under the strategic direction of General Maksim A. Purkayev’s Far Eastern Front, with command on the island exercised by General Leytenant Leonti G. Cheremisov’s 16^th Army, whose primary asset was General Major Anatoli A. Diakonov’s LVI Corps (79^th Division, 2^nd, 5^th and 113^rd Brigades and 214^th Tank Brigade), and the 255^th Composite Aviation Division (106 aircraft). Also available were the forces of Admiral Ivan S. Yumashev’s Pacific Fleet, which comprised Vitse Admiral Vladimir A. Andreyev’s Northern Pacific Flotilla, the Pacific Fleet’s 80 aircraft and the 365^th Naval Infantry Battalion.

The Japanese defence, in line with the 'Sho 4' strategic defence plan, was based on General Kiichiro Higuchi’s 5^th Area Army. This formation was tasked with the defence of Hokkaido island, the Kurile islands group and southern Sakhalin, and for the last relied on the 88^th Division, which had been established on 28 February 1945 in Yuzhno-Sakhalinsk as a 20,000-man triangular division on the basis of the 'Karafuto' Independent Mixed Brigade. The fixed defences were centred on the Cotonou Fortified Area (17 bunkers, 28 artillery positions, 18 mortar positions and other elements), 5,400 men of the local border guard, and a number of reservist detachments, of the 'Karafuto' Fortress Defence Line'.

On 11 August, the 20,000 men and 100 armoured fighting vehicles of the 16^th Army began the 'South Sakhalin Offensive Operation' from northern Sakhalin, but despite enjoying a local superiority of about 3/1, were quickly brought to a halt by the sturdy Japanese defence of the 'Karafuto' Fortress Defence Line. The Soviets were held back for four days until, on 15 August, the Imperial Japanese Headquarters ordered the end of all offensive combat operations in favour of ceasefire negotiations. Yet the 5^th Area Army issued a countermanding order to the 88^th Division, which was instructed to defend Sakhalin to the last man. On this same day, however, 3,000 Japanese troops surrendered the 'Karafuto' Fortress Defence Line after losing 568 men killed.

In order to accelerate the invasion of Sakhalin island and to relieve pressure on the ground invasion from the north, the Soviet navy launched an amphibious assault operation from Sovetskaya Gavan on the Siberian mainland against the key Japanese ports on the east and south coasts of southern Sakhalin island, on which a naval blockade was also instituted in order to prevent the evacuation of Japanese troops. Japanese convoys were also targeted by Soviet submarines in the Gulf of Aniva.

On 16 August, the Soviet coast guard ship Zarnitsa, four minesweepers, two transport vessels, six gunboats and 19 motor torpedo boats arrived in Toro (now Shakhtyorsk) on the north-west coast of Japanese-held southern Sakhalin, where they landed about 1,400 men of the 365^th Separate Marine Battalion and one battalion of the 113^th Brigade to engage the Japanese garrison of 200 men. Toro was captured and on the following day the Soviets took another four populated areas and the port city of Esutoru (now Uglegorsk), Anbetsu (now Vozvrashcheniye) and Yerinai. The Japanese casualties were 100 men killed, 150 wounded and 30 captured, while the Soviet casualties were 12 men killed.

On 20 August, 3,400 men of a Soviet naval combined marine battalion and the 113^th Brigade landed in Maoka (now Kholmsk), farther to the south on the west coast of Sakhalin. The Japanese forces in the port and city were two infantry battalions, several artillery and mortar units, and coast guard elements, all under the overall command of the 88^th Division.

After a Soviet submarine and aviation reconnaissance on 17 August, on 19 August an amphibious force of the 113^th Brigade and one battalion of marines, totalling 3,400 men, departed Sovetskaya Gavan in eastern Siberia and landed at Maoka early in the morning of 20 August. As a result of heavy fog the Soviet forces had no air support, but the port and city were subjected to heavy naval gunfire attack. Tactical surprise meant that the Soviets were able to take the coastal facilities quickly and without significant opposition, but later the Soviet troops were met with fierce Japanese resistance, according to Soviet accounts, although Japanese accounts suggest that the Japanese military tried to avoid engagement by keeping to its defensive positions, aiding the removal of equipment and supervising the evacuation of about 18,000 civilians.

After the success of the assault, between 22 and 24 August Soviet reinforcements arrived from Vladivostok and proceeded to clear the Japanese forces from the southern part of Sakhalin. According to refugees already evacuated from the area, Soviet forces carried out potent naval gunfire and artillery attacks against Japanese installations in Maoka, Shikuka and groups of civilians awaiting evacuation, resulting in the deaths of about 1,000 civilians. Witnesses reported that many of the fatalities were attributable to confusion in the minds of the Soviets by the general use among male civilians of the kokumin-fuku, men’s approved clothing bearing a close resemblance to military uniforms.

A number of telephone operators at the city post office opted not to be evacuated, and these maintained contact with the city of Wakkanai on Hokkaido, as well as mainland Japan, until the moment that Soviet forces destroyed the city’s postal and telephone buildings. On 20 August, fearing that they would be raped by the Soviet invaders, nine of the 12 female operators killed themselves with poison, and the other three were saved by their male colleagues' intervention. The survivors at the post office were treated well by the Soviets.

On 21 August the advent of better weather allowed the Soviets to operate warplanes over the 'South Sakhalin Offensive Operation', but despite this fact the Japanese continued their resistance after receiving an order to cover the evacuation.

Some Soviet naval vessels were damaged by Japanese shore artillery, which led to a Soviet gunfire bombardment of the city, causing approximately 600 to 1,000 civilian deaths. The Soviets completed their seizure of Maoka on 22 August in the face of heavy Japanese resistance throughout the city. Japanese military casualties in this battle were 300 killed and 600 captured, while the Soviet casualties were 60 army and 17 naval troops killed.

On 25 August, 1,600 Soviet troops landed at Otomari (now Korsakov), at the head of the Gulf of Aniva on the south coast of Sakhalin. Here the 3,400-man Japanese garrison surrendered, and on the same day the remnants of the 88^th Division surrendered to the 16^th Army and the city of Toyohara, just to the north of Otomari, was captured without resistance as the forces of the 16^th Army drove to the south from the island’s dividing line, officially ending the 'South Sakhalin Offensive Operation'.

The Japanese casualties were in the order of 700 to 2,000 soldiers killed and 3,500 to 3,700 civilians killed. About 18,202 Japanese troops were taken prisoner, many of them being despatched to labour camps in Siberia and held after the war. At least 100,000 Japanese civilians fled the Soviet occupation during the invasion. The 16^th Army’s losses have never been published, and those of the Pacific Fleet were 89 men killed. The capture of Sakhalin island proved the springboard for the 'Kurile Islands Landing Operation'. Following the Japanese surrender, the southern part of Sakhalin island became Soviet territory.