Summary

Czechoslovak National Council The Czechoslovak flag, historic coat of arms of the Czechoslovak lands (1918)

The Slovaks of Hungary have lately been using the so-called “Pan-Slavic” tricolor, which. however, is properly Russian. In the Manifesto of the Slovak Constituent Assembly (Liptovsky Sv. Mikulas May, May, 1848) , the right to use the white and red as the national colors of Slovakia was made one of the chief demands.
Source: Wikisource

Czechoslovak National Council The Czechoslovak flag, historic coat of arms of the Czechoslovak lands (1918)

Hence the white-red flag is both the national and the battle flag of the Czechoslovaks.
FLAG OF THE CZECHOSLOVAK NATIONAL COUNCIL
The future Diet of the Czechoslovak State alone can adopt an official flag for the State. During this war the Czechoslovak National Council, the provisional government of the Czechoslovaks, has adopted as its official colors white and red in a blue field. In the center are the initials Č S, the insignia of the Czechoslovak armies in France and Italy. The blue field is taken from the color of the three mountains Tatra, Matra and Fatra on the Slovak coat of arms.
Source: Wikisource

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