Upon graduation from West Point in 1913, Brewer was commissioned as a Second lieutenant and was assigned to the 3rd Field Artillery at Fort Sam Houston, serving along the Texas border until 1916 during the Mexican Revolution. In March 1916, he went with the 4th Field Artillery to the Panama Canal Zone. From August 1916 through 1921, he taught in the Department of Mathematics at the U.S. Military Academy at West Point. In 1920, he was promoted to Major. From 1921 through 1924, he went to the 8th Field Artillery in Hawaii.
Brewer studied at the Advanced Course at the Field Artillery School at Ft. Sill, Oklahoma, in 1926–1927, and then graduated at the top of his class at the Command and General Staff College in Fort Leavenworth (1927–1928). He went back to the Field Artillery School in 1928 and taught in the Gunnery Department, becoming the Director of the department. His immediate predecessor as head of the Department of Gunnery, who was also an instructor when Brewer took advanced coursework there, was Jacob Loucks Devers, who would remain a lifelong friend and later prove providential in the course of his career.
Brewer had missed combat duty during World War I because he had been on the faculty teaching at West Point and was not enamored with having a non-combat command again. He requested termination of his rank of Major General and permanent reversion to the rank of Colonel, then he wrote to General Jacob Devers who had been his instructor at Field Artillery School, whom he replaced as its director, and for whom he served as Chief of Staff with the 9th Infantry Division, “Old Reliables”. Devers was in command of the newly formed Sixth United States Army Group leading the Allied invasion in the south of France, which consisted of the 7th Army under General Alexander Patch and the First French Army under Geneneral Jean de Lattre de Tassigny. His former command, the 12th Armored Division was assigned to the 7th Army. Brewer asked Devers if as a Colonel he could command the newly formed 46th Group Heavy Army Artillery assigned to the 7th Army, commanded by Patch who had been in the same graduating class at West Point and with whom he served under Jacob Devers with the 9th Infantry Division. The 46th Field Artillery Group under Colonel Brewer began its combat operations in January 1945 in the Vosges Mountains, providing heavy artillery support for the VI Corps, commanded by Major General Edward Hale “Ted” Brooks. They continued support of the Corps through its advance into Germany through the Siegfried Line, across the Rhine river, through the Black Forest and into Bavaria. Their combat ended at Garmisch when the Germans surrendered on 08-05-1945.
Death and burial ground of Brewer, Carlos.
Brewer served in the Army of Occupation under the command of General Geoffrey Keyes as the Seventh Army Artillery Officer and as Headquarters Commandant & Commander of the Heidelberg Area Command in Germany from 1946 to 1947. From 1947 to 1950, he was Professor of Military Science & Tactics at Ohio State University where he ran the ROTC Program. He retired from the military in 1950, but continued working for the Ohio State Research Foundation from 1950 to 1960 as a consultant on classified military research contracts.
He married Grace Moore (1891–1956) on 20-12-1913. They had four children: Carlos Jr., Edward, Robert, and Grace Elizabeth Brewer Schulten. After the death of his first wife from tuberculosis in 1956, he married Mary Taylor Williams in 1959. At West Point, he was on the polo team, was an expert marksman, and was on the broadsword team. He also was an avid chess player, and was one of twenty players at West Point who played simultaneous games against nine-year old Polish chess prodigy Samuel Reshevsky in 1920. Reshevsky won 19 of the 20 games, including the game against Brewer, which lasted just under two hours
Major General Brewer, Carlos died 29-09-1976, aged 85, in Columbus, Ohio and is buried at Arlington National Cemetery, Virginia, VS, Section 30 Lot 876.