[1] In June 1941, Helmick was transferred to the Army of the United States and assigned the rank of Colonel, serving as chief of the Budget Branch of the Department of War's General Staff.

He led the naval bombardment of Omaha Beach, allowing for shore batteries to be established by American troops.

Following the end of the war, Helmick was awarded the Army Distinguished Service Medal for "exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility as V Corps Artillery Commander during the campaigns of Ardennes, Rhineland, and Central Europe, December 1944 to May 1945.

In 1948 he was called to South Korea by General John R. Hodge to partake in Operation Blacklist Forty as American military governor.

During his tenure, Helmick oversaw the U.S. purchase of Japanese property in Korea to be sold to the Korean government of Syngman Rhee.