That is incorrect. The USSR was composed of 13 states. Two of which are Ukraine and Russia. Post WWII, Crimea had been part of Russia until Khrushchev gave it back to Ukraine in 1954.
“On 19 February 1954, the oblast was transferred from the Russian SFSR to the Ukrainian SSR jurisdiction,[52] on the basis of "the integral character of the economy, the territorial proximity and the close economic and cultural ties between the Crimea Province and the Ukrainian SSR"[53] and to commemorate the 300th anniversary of Ukraine's union with Russia.[54][55]
Sevastopol was a closed city due to its importance as the port of the Soviet Black Sea Fleet and was attached to the Crimean Oblast only in 1978.”
-Wikipedia (Crimea history)
It’s important to know that Ukraine, and especially Crimea, have been the Grand Central station of occupation by outside powers for centuries. Ukraine and Crimea had been subjected to ethnic cleansing by the Soviets.