[2] The younger McGlachlin was educated in Wisconsin, and graduated 20th in a class of 49 from the United States Military Academy (USMA) at West Point, New York in June 1889.

[4] In 1904 he was ordered to the Philippines during the U.S. occupation, and received the Silver Star Citation for heroism at the First Battle of Bud Dajo during the Moro Rebellion.

[7] McGlachlin was promoted to brigadier general on August 5, 1917, almost four months after the American entry into World War I, and commanded the 165th Field Artillery Brigade, 90th Division at Camp Travis, Texas during its initial organization and training.

He was later appointed Chief of Artillery for the First Army, and he served in that position until the end of the war on Armistice with Germany on November 11, 1918.

He commanded the 1st Division near the end of the war,[9] and American Forces in Germany during the post-war Allied occupation of the Rhineland.