Flag of the Ukrainian Soviet Socialist Republic

The first flag of the Ukrainian Soviet Socialist Republic (UkrSSR) was adopted on 10 March 1919 to serve as the symbol of state of the Ukrainian SSR. Details of the official flag changed periodically before the collapse of the Soviet Union in 1991, but all had as their basis the communist red flag. According to the decree of the Presidium of Supreme Soviet of Ukrainian SSR on 21 November 1949, the blue in the bottom "symbolises the mightiness and beauty of the people, and the blue banner of Bohdan Khmelnytsky".

Source: Wikipedia — Flag of the Ukrainian Soviet Socialist Republic (CC BY-SA 4.0)