Shortly thereafter Lerch was drafted into the Officers Reserve Corps and commissioned a Second Lieutenant, assigned to the 63rd Infantry Regiment.

[1] Following the end of World War I, Lerch attained the rank of Captain and was stationed in California, the Philippines, and Hawaii.

He served as a legal advisor to the Hawaiian Public Works Administration, and was promoted to the rank of Major in August 1935, after which he underwent further infantry training at the U.S. Army's Command and General Staff School in Fort Leavenworth.

[2] He obtained a Bachelor of Laws from George Washington University in 1942 and was subsequently admitted to the American Bar Association.

[2][4] Following his service as a Provost Marshal, Lerch participated in Operation Blacklist Forty, serving with the Eighth Army as the American Military Governor of Korea.