Stalin had been waiting for years to have his revenge for the humiliating defeat that the Red Army had suffered during the final stages of the Civil war. Stalin wanted to recover the lands that made up the Kingdom of Ukraine and Belorussia. He had been assured by the Soviet Army General staff that the Red Army was ready to launch the Massive recovery Campaign.
Stalin wanted to know was there enough forces available to assure that the Red Army would win. Currently the Red Army forces that were assigned to this mission totaled 65 Rifle Divisions, 40 Tank Battalions, 12 Cavalry divisions and 6 artillery divisions but Stalin felt that this was not enough and order more forces assembled for the invasion, As a result the launch date was postponed from May 1st to the 21st of that Month. By the time that the last division arrived the Red Army would have assembled 85 Rifle Divisions,85 tank battalions and 18 cavalry divisions supported by 18 artillery divisions. The Red Air Force would provide massive support to the invasion. The blows would start with a drive into the eastern Ukraine and then a week latter a blow would hit Belorussia.
The Ukrainian army had been training ever since the Civil war but it maintained a much smaller active duty force of just 18 divisions. However, 6 of those divisions were rather large- 20,000 men strong. These were the elite of the Ukrainian army equipped with the Vickers E tank and the Czech T-35 . The other 12 divisions had 15-18000 but depended upon older tanks or tanks armed with machine guns. The Ukrainain army also had Horse cavalry units.