After considerable wrangling back and forth with the authorities, Nathaniel Lyon managed to get official permission to enlist Unionist Germans into the Army to protect the St. Louis Arsenal. Again, check out Damned Yankee: The Life of General Nathaniel Lyon for more on Lyon and Missouri.
Washington, April 21, 1861.
Capt. N. LYON, Second Infantry, East Saint Louis:
General Harney has this day been relieved from his command. The Secretary of War directs that you immediately execute the order previously given to arm the loyal citizens, to protect the public property, and execute the laws. Muster four regiments into the service.
OR Ser 1, Vol. 1, p. 641