[8] From June to July 1917, Pennell was assigned to World War I duty with the 18th Field Artillery Regiment at Fort Bliss, Texas.

[8] The Armistice of November 11, 1918 ended the war, and in December Pennell was assigned to duty in Europe as a member of the Armament Board, which was chaired by Brigadier General William I.

[9] He was then assigned as a student at the United States Army Command and General Staff College, which he completed in August 1923 as a Distinguished Graduate.

[9] From February 1924 to August 1926, he served as the Chief of Field Artillery's liaison officer to the Ordnance Corps at Aberdeen Proving Ground, Maryland.

[9] In December 1930, he was assigned to the Eighth Corps Area at Fort Sam Houston, Texas as assistant chief of staff for logistics (G-4).

[6] In February 1935, he assumed command of the 15th Field Artillery at Fort Bragg, North Carolina, and in August he received promotion to colonel.

[6] In October 1940, Pennell was assigned to Fort McClellan, Alabama as commander of the 52nd Field Artillery Brigade, a unit of the 27th Infantry Division.

[6] In January 1941, he was promoted to brigadier general, and he continued to lead the brigade during its pre-World War II organization and training.

[6][10] In October 1942, Pennell was assigned to Newark, New Jersey as a member of the War Department Dependency Board, which established policies and procedures with respect to releasing information about killed and wounded soldiers to next-of-kin.

[6] He received a second award of the Distinguished Service Medal for his command of the 52nd Field Artillery Brigade, 27th Infantry Division, and Hawaii District.

31 (1922)[11] The President of the United States of America, authorized by Act of Congress, July 9, 1918, takes pleasure in presenting a Bronze Oak Leaf Cluster in lieu of a Second Award of the Army Distinguished Service Medal to Major General Ralph McTyeire Pennell (ASN: 0-2150), United States Army, for exceptionally meritorious and distinguished services to the Government of the United States, in a duty of great responsibility as Commanding General of an Infantry Division in the Hawaiian Department during the period 15 March 1942 to 1 November 1942.

By outstanding ability, leadership, and energy, General Pennell brought his Division to a high degree of training and readiness for combat conditions.

By reason of his qualities as an officer, a very difficult situation was handled in a superior manner and military civilian relationships were greatly improved.

As commandant of the field artillery school he carried out many important projects including the Metro Augmentation program,[a] the expansion of the department of air training, the field artillery radar program and the redeployment short courses for officers and enlisted men scheduled for combat in the Pacific area.

[6] He died in Atlanta, Georgia on May 17, 1973 after he was stricken with a heart attack at the city's airport while en route to a family reunion in South Carolina.