The 5th Corps was formed from the Transbaikal Cossacks and various other volunteer forces fighting under Ataman (chief) Grigory Semyonov, as part of his Special Manchurian Unit (Особый маньчжурский отряд, OMO).
[1] After Grigory Semyonov's OMO, based in Chita and sponsored by Japanese intervention forces, made contact with the Provisional Siberian Government under Pyotr Vologodsky in September 1918, he was promoted by the Omsk government's war minister Pavel Ivanov-Rinov to the rank of colonel and was designated as the commander of the 5th Pri-Amur Army Corps.
[3] There was friction between Semyonov's loyalists in the OMO and the other units of the 5th Corps that were more loyal to the Provisional Siberian Government, and they viewed each other with suspicion.
[4] When Admiral Alexander Kolchak, a rival of the ataman and his Japanese backers, took control of the Siberian government in a coup, the hostility between the two factions escalated.
[5] In addition to Semyonov's OMO, which consisted of some 5,000 men, the 5th Corps also included the following in its order of battle as of October 1918:[3][4] The 5th Corps consisted of a variety of different nationalities, with a large number of Mongols, Chinese, and indigenous Siberian peoples, as well as mercenaries and recruits from European countries, such as Belgium, Serbia, and Romania.