Walsh worked at a variety of occupations before becoming a full time member of the Minnesota National Guard as assistant adjutant general after World War I, including farm laborer and auditor.

The 1st Infantry was mustered into federal service on June 30, 1916, for duty at Camp Llano Grande, near Mercedes, Texas, on the Mexico–United States border.

In 1929, Walsh was tasked to locate a new training facility site for the Guard, and selected a 12,000 acre area near Little Falls, Minnesota.

Minnesota Governor Floyd B. Olson activated the National Guard, and Walsh commanded 4,000 Guardsmen in the suppression of the chaos.

Utilizing roving patrols, curfews, and security details, Walsh quickly restored order, thus enabling negotiated settlement of the labor dispute.

Governor Harold E. Stassen called in the National Guard, and Adjutant General Walsh commanded 300 Guardsmen who patrolled the streets and imposed a quasi-martial law while the community was stabilized.

As the potential of U.S. involvement became more evident, the Franklin D. Roosevelt administration still hoped to avoid war, while military leaders needed to prepare to fight.

The division was transported by rail and truck convoys to the newly constructed Camp Claiborne in Rapides Parish, Louisiana, near Alexandria.

[7] In the early phase of the maneuvers, Walsh, who suffered from chronic ulcers, became too ill to continue in command, and was replaced by Major General Russell P. Hartle on August 5, 1941.