The Ussuri Host was the most easternmost of all the Cossacks. Their settlements were between Vladivostok and Khabarovsk, in the Primorye province, along the Ussuri River, the Sungari River, and around the Khanka Lake. It was a small host, only 30 years old.
The Ataman of the Ussuri Host in Tsarist times was also military governor of the region, which gave the title rather more importance in the Civil War than most Atamans.
The Ussuri Host had been formed from a unit of the Amur Host, and its colours were also yellow and green, though arranged differently.
The Ussuri Host held several grand krugs in 1917 to discuss what to do about the revolution, but no firm decisions were made as the host was divided in its approach. As a result no attempt was made to stop the Bolshevik takeover of the towns in the area.
The general attitude was reversed in January 1918 at another krug, even though by now many frontoviki had returned home. The reactionary Ivan Kalmykov was elected as Ataman, representing the bulk of villagers and elders, refusing to accept the Soviet takeover and demanding the retention of Cossack privileges. But a sizable rump, dominated by soldiers, opposed Kalmykov and supported the Bolsheviks.
While not supporting Soviet power in their own villages, few Ussuri Cossacks were prepared to fight them elsewhere. Instead Kalmykov turned to the Allies, especially Japan, and received large quantities of both money and weapons. He formed the Special Cossack Detachment, or OKO with a couple of hundred men.
In July he moved to take over the Ussuri region from the Red Guards and their "Internationalist" allies. He had no chance of defeating the much more numerous Reds by himself, and in fact he struggled to even clear the Cossack villages of Soviet sympathisers. But luckily for him it was at this time that the Czechs were just clearing the Trans-Siberian, and the Japanese were establishing themselves in the Maritime province. Thanks almost entirely to them them the Reds were forced to retreat north.
The Reds formed a line at Kraevski. A confrontation between Allied forces - British, French, Czech and Cossack - and the Reds ended in stalemate. It was only after the Japanese started to actively engage that the Reds were driven off. Thanks to them in September Kalmykov was able to enter Khabarovsk. All Red forces were liquidated or forced to hide in the taiga.
Kalmykov now commenced a counter-revolutionary repression, supported by Japanese money and 1,600 soldiers, only a small portion of whom were actually Cossack. The pre-war Cossack officers had either stayed on with Semenov when they passed through the Trans-Baikal, or moved to Vladivostok, so he lacked solid leadership as well as troops. What few Cossacks were drafted were unreliable in battle, and increasingly prone to mutiny and desertion.
Although formally subordinating himself to Ataman Semënov in Chita, in practice Kalmykov ruled the Maritime province as a personal fiefdom. He also tried to extend his rule towards Blagoveshchensk, but was unable to penetrate Vladivostok, which had a much more moderate White regime.
As Kalmykov and his men plundered, killed and raped with incredible rapacity, the support for the Red partisans in the taiga multiplied. Attempts to suppress the them were so random and brutal that they were counter-productive. It was clear that only Japanese money and bayonets allowed the regime to survive.
In May 1919 the 36th Siberian Rifle Regiment was stationed in Khabarovsk and available for service, but in general the Ussuri forces were politically and militarily separate throughout the war. Indeed Kalmykov actively prevented material from reaching Kolchak in order to enrich himself.
By the end of 1919 the Primorye partisans had heard of Kolchak's fall and were greatly emboldened, and started to attack the main towns. Their advance was barely opposed as the White troops mutinied or deserted. By February 1920 all of Primorye was in Red hands. Kalmykov fled to China and was captured. Vladivostok itself fell to the Provisional Zemstvo Government, which was relatively moderate, if more Bolshevik than White in orientation. Elsewhere though Red Terror quickly replaced the White variety.
At the end of December 1918 the Ussuri Cossack Host forces were, at least on paper: an HQ detachment; a Plastoon Battalion (3 sotnias, officer platoon, training unit); the 1st Ussuri Cossack Regiment (4 sotnias, a training unit); the 2nd Ussuri Cossack Regiment (4 sotnias, MG team from February); a Horse-mountain Divizion of 2 batteries; a Cadet Battery, a Separate Heavy Battery; Artillery Scouts; the armoured train "Kalmykovets; an Engineer Company; an MG command and the Escort to the Ataman.
By October the forces were the Detached Ussuri Cossack Ataman Kalmykov Brigade, composed of: an HQ; the Ussuri Cossack Regiment; some separate Ussuri Mounted Sotnias; some Volunteer Cavalry Sotnias, some Native Horse Sotnias, a Horse Artillery Divizion; two armoured trains; and an Engineer Divizion. Three infantry battalions were being raised, mostly from former Red Army prisoners sent from the main Siberian front. The 36th Siberian Rifle Regiment was also available.
The forces did not change significantly until the final collapse in winter 1920. The Cossack Cavalry became the Ataman Cossack Regiment, and the separate sotnias were regrouped a bit, becoming a Horse Divizion. Kalmykov called a general mobilisation late in 1919 as the partisans became more threatening, but apart from a few local self-defence units, turnout was minimal.
The Ussuri Host never mobilised as a whole, and many of the men serving in these units were not Cossacks. In fact many Cossacks did everything they could to avoid service in Kalmykov's army, which was notorious for its indiscipline and atrocities. The result was that as a military force the Ussuri Brigade was pretty much useless. Without the Japanese to do the real work, they would quickly have collapsed. They never did fight the regular Red Army.
Obviously when the White regrouped in Primorye in late 1921 there were some Ussuri Cossacks, but once again they were very reluctant to serve in the White forces. An infantry divizion and a cavalry sotnia seem to be all they could muster.
Jamie Bisher, "White Terror: Cossack Warlords of the Trans-Siberian", Routledge, 2005