With the end of World War I in 1918, the Air Service, United States Army was largely demobilized. During the demobilization period of 1919, the Regular Army and its air arm answered a call to defend the southern border against raids from Mexico, and to halt smuggling of illegal aliens and narcotics into the United States and weapons from the United States into Mexico.
Background
see also Pancho Villa Expedition
Revolution and disorder in Mexico and trouble along the U.S.-Mexican border in March 1913 brought on the hurried organization of the 1st Aero Squadron, the U.S. Army's first tactical unit equipped with airplanes. In 1916 the squadron took part in General Pershing’s Punitive Expedition into Mexico in pursuit of Mexican revolutionist Pancho Villa.
Difficulties along the border continued during World War I while the United States was at war in Europe. Mexican bandits often raided American ranches to secure supplies, cattle, and horses, and in doing so sometimes killed the ranchers. U.S. troops stationed along the border shot raiders as they pursued them into Mexico. The biggest clash came in August 1918, when more than 800 American troops fought some 600 Mexicans near Nogales, Arizona.
Border patrol was one of the many activities being considered for the postwar United States Army Air Service. However, no aviation units had been assigned to duty on the Mexican border, when a large force of Villistas moved northward in June 1919 toward Ciudad Juarez, Chihuahua, Mexico (opposite El Paso, Texas), garrisoned by Mexican government forces. Major General DeRosey C. Cabell, Commanding General of the Army Southern Department, received orders to seal off the border if Villa took Juarez. If the Villistas tired across the border, Cabell was to cross into Mexico, disperse Villa's troops, and withdraw as soon as the safety of El Paso was assured. The general ordered Air Service men and planes from Kelly Field and Ellington Field, Texas, to Fort Bliss, near El Paso, for border patrol.
American troops under Brig. Gen. James B. Erwin, Commander of the El Paso District of the Southern Department, were on alert when about 1,600 of Villa's men attacked Juarez during the night of 14/15 June 1919. Stray fire from across the river killed an American soldier and a civilian, and wounded two other soldiers and four civilians. Around 3,600 U.S. troops crossed into Mexico, quickly dispersed the Villistas, and returned to the American side.
Air Service surveillance mission
As a result of this incident, Air Service personnel equipped with war surplus Dayton-Wright DH-4 aircraft were ordered to Fort Bliss, Texas, on 15 June. Major Edgar G. Tobin, an ace who had flown with the 103d Aero Squadron in France, inaugurated an aerial patrol on the border on the 19th. By mid-September the force grew to 104 officers, 491 enlisted men, and 67 planes from the 8th Surveillance Squadron, 9th Corps Observation Squadron, 11th Aero Squadron, 90th Aero Squadron and the 96th Aero Squadron.
In the summer of 1919, the Air Service planned to assign at least nine Aero Squadrons and one Airship Company for surveillance of the entire Mexican border from the Gulf of Mexico to the Pacific Ocean. The original plan called for two Observation Squadrons (the 9th and 91st) of the Western Department to patrol eastward from Rockwell Field, California, to the California-Arizona line. Three Surveillance Squadrons (the 8th, 90th, and 104th) and four Bombardment Squadrons (the 1lth, 20th, 96th, and 166th) of the Southern Department were to be distributed along the border from Arizona to the Gulf of Mexico.
On 1 July 1919, three surveillance squadrons were organized into the Army Surveillance Group (ASG) headquartered at Kelly Field. In September the four bombardment squadrons formed the 1st Day Bombardment Group, also with headquarters at Kelly Field. In addition the 1st Pursuit Group and its squadrons (27th, 94th, 95th, and 147th) were moved from Selfridge Field, Michigan, to Kelly at the end of August to be available if needed. The three groups (surveillance, day bombardment, and pursuit) comprised the 1st Wing at Kelly. Commanded by Lt. Col. Henry B. Clagett, the 1st Wing became responsible for aerial patrol of the border in the Southern Department. Also in August, work started on a large steel hangar for an airship station at Camp Owen Bierne, Fort Bliss (which later became part of Biggs Field).