In 1918, Celmiņš enlisted into the newly created Latvian Army, and was promoted to lieutenant the following year, and was then appointed Latvian military attaché in Poland.
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On 24 January 1932, the Latvian nationalist group Ugunskrusts was founded, and Gustavs Celmiņš was elected as its leader.
Pērkonkrusts, the Latvian fascist organisation led by Gustavs Celmiņš, is also sometimes referred to in English as the Thunder Cross.