During World War I he saw action in France, and was awarded the Purple Heart for wounds received in action. He was commissioned a second lieutenant in May, 1917, and made Captain of field artillery in December 1917. He served in Germany with the Army of Occupation.
His spectacular career as a Marine started in 1922 when he enlisted as a private. In 1923 he was commissioned a second lieutenant. After duty at Quantico, Virginia, he sailed for Culebra, Puerto Rico, in 1924 and remained there five months before being ordered to the West Coast for duty with the Pacific Fleet. Applying for aviation training in 1925, he went to Pensacola, Florida, for instruction, but subsequently returned to duty with ground units. He served another tour of foreign shore duty from 1927 to 1929 at Shanghai, China.
First Lieutenant Carlson was ordered to Nicaragua in 1930 as an officer in the Guardia Nacional. It was there, he earned his first Navy Cross for leading 12 Marines against 100 bandits. He also was commended for his actions following the earthquake at Managua in 1931, and for performance of duties as Chief of Police in 1932 and 1933.
Returning to the United States in 1933, he was sent almost immediately to Shanghai. Shortly afterward he was transferred to the Marine Detachment, American Legation, Peiping, China, where he served as Adjutant and studied the Chinese language. In 1936 he returned to the United States via Japan. At home he served at Quantico while attending Marine Corps Schools, and studying International Law and Politics at George Washington University in Washington, D.C.
He went back to China for the third time, in 1937, as an official student of the Chinese language and as a military observer with Chinese forces. There he was afforded the opportunity to learn the tactics of the Japanese soldier.
Traveling thousands of miles through the interior of China, often on foot and horseback over the most hazardous terrain, he lived under the primitive conditions of native troops. When he left China in 1938, he was commended by the Commander in Chief of the Asiatic Fleet for his services.
He was so impressed with the danger of Japanese aggression in the Far East that in 1939 he resigned his commission as a captain in order to be free to write and lecture on that subject. When the danger he foresaw neared reality in 1941, he applied to be recommissioned in the Marine Corps and was accepted with the rank of major. A year later he was placed in command of the Second Marine Raider Battalion with the rank of lieutenant colonel. His leadership of that unit in the raid on Makin Island, 17 August 1942, earned him a Gold Star in lieu of a second Navy Cross. A second Gold Star was awarded him for heroism and distinguished leadership on Guadalcanal in November and December of that year.
He was ordered back to the United States for medical treatment in the Spring of 1943, and subsequently returned to Tarawa as an observer. In that engagement he was cited for volunteering to carry vital information through enemy fire from an advanced post to division headquarters.
He was wounded during the Saipan operation while attempting to rescue a wounded enlisted man from a front line observation post, and was awarded a Gold Star in lieu of a second Purple Heart. Physical disability resulting from the wounds received on Saipan caused the his retirement on 1 July 1946. He was advanced to the rank of brigadier general on the retired list at that time for having been specially commended for the performance of duty in actual combat.
On 27 May 1947, the 51-year-old veteran succumbed to a heart illness at Emmanuel Hospital, Portland, Oregon. He had been living in Brightwood, Oregon, since his retirement.
In addition to the Navy Cross with two Gold Stars in lieu of a second and third award, and the Purple Heart with a Gold Star in lieu of a second award, BGen Carlson was awarded the Legion of Merit; Presidential Unit Citation with three Stars; World War I Victory Medal with France Clasp; World War II Victory Medal; China Service Medal; Yangtze Service Medal; Expeditionary Medal; Italian Croix de Guerre; Nicaragua Presidential Order of Merit; Nicaraguan Medal of Distinction; Second Nicaraguan Campaign Medal; Asiatic-Pacific Campaign Medal with three Bronze Stars; American Campaign Medal; and the American Defense Service Medal.