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.Army Hist Div, Order of Battle, 111, pt 1, 610–11.Clarence C. Clendenen, Blood on the Border: The United States Army and the Mexican Irregulars (London, 1969), pp 351–355

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).ASNLs, Sep 3, 1919, pp 1–2, Dec 3, 1919, p 1.

Operations The Air Service soon scaled down the plan for border patrol. Although minor incidents continued to occur, Pancho Villa never succeeded in rebuilding his forces. The major threat had been dispelled by the time aerial patrol began. From January 1920 on, the mission of the Mexican Border Patrol in the Southern Department was assigned to the 1st Surveillance Group that had moved its headquarters to Fort Bliss and gained an extra squadron, the 12th. The group's squadrons operated in two flights, each patrolling a sector on either side of its operating base.

From the Gulf of Mexico westward, the deployment was as follows:

8th Aero (later Surveillance, later Squadron) (Attack) Headquarters, Kelly Field, San Antonio, Texas, 25 May 1919 Flight operated from: McAllen Field, Texas, after 25 July 1919 Headquarters moved to: McAllen Field, Texas, 13 August 1919 Flight operated from: Laredo Field, Texas, 15 August 1919 Squadron re-combined at: Kelly Field, Texas, 2 July 1921

The 8th's patrol sector was from the mouth of the Rio Grande at the Gulf of Mexico to Eagle Pass, Texas.

90th Squadron (Surveillance) Headquarters, Kelly Field, San Antonio, Texas, 15 May 1919 Flight A operated from: Eagle Pass Field, Texas, 27 August 1919 Flight B operated from: Kelly Field No. 2, Texas, 30 September-29 November 1919 Headquarters moved to: Sanderson Field, Texas, 29 November 1919 Flight A operated from: Eagle Pass Field, Texas, to 12 June 1920 Flight A operated from: Del Rio Field, Texas, 12 June 1920 – 30 June 1921 Squadron re-combined at: Kelly Field, Texas, 2 July 1921

The 90th's patrol sector was from Eagle Pass to Lajitas, Texas.

104th Surveillance Squadron (later 13th Squadron (Attack)), 25 May 1919 Headquarters, Kelly Field, San Antonio, Texas, 1 June 1919 Headquarters, Fort Bliss, Texas, 6 November 1919 Flight operated from: Marfa Field, Texas, 6 November 1919 – 3 September 1920 Flight operated from: Marfa Field, Texas, 17 November 1920 – 30 June 1921 Squadron re-combined at: Kelly Field, Texas, 2 July 1921

The 13th's patrol sector was from Lajitas to El Paso, Texas

12th Aero, (later 12th Squadron (Observation) ) Headquarters, Fort Bliss, El Paso, Texas, 9 January 1920 Flight operated from: Douglas Field, Arizona from 10 January 1920 Headquarters moved to: Nogales Field, Arizona, 12 April 1920 Flight operated from: Douglas Field, Arizona from 12 April 1920 Headquarters moved to: Douglas Field, Arizona, 1 February 1921 Flight operated from: Nogales Field, Arizona from 1 February 1921 Squadron re-combined at Biggs Field, Texas, 28 September 1921

The 12th's patrol sector was from El Paso, Texas to Yuma, Arizona

Western Department Area: Jones Chronology, Jun 18, 1919.Maurer, Combat Squadrons. Maps of the Army's patrol districts are found in Army Historical Division, Order of Battle, 111, part 1, following pages 606, 608, and 616. 9th Corps Observation Squadron Operated from: March Field and Rockwell Field, California, 22 July 1919 – 27 April 1920 Flight operated from Calexico Field, California, 22 July 1919 – 1 April 1920

91st Aero (later 91st) Squadron Operated from: Ream Field, California, 24 January 1920 Flight, or detachment thereof, operated from El Centro Field and Calexico Field, California, 17 March – 30 July 1920 Squadron re-combined at: Rockwell Field, California, 30 April 1920

Both the 9th and 91st patrolled from the Pacific Coast at San Diego along the border to Yuma, Arizona.

The border patrol mission started with DH-4s and Curtiss JN-4 Jennies, with both eventually replaced with updated Dayton-Wright DH-4Bs. Most of the first planes were not properly equipped for field service. Not knowing what turn events on the border might take, the Army wanted the planes ready for any eventuality. Colonel James E. Fechet, Air Service Officer at the Southern Department, found it no easy task to obtain bomb racks, machine gun mounts, cameras, and other equipment. There was a delay, for example, in installing synchronized Martin guns because parts supplied with the guns did not fit the planes on the border. The radios on some planes could send only in code and could not do that very well. Compasses were unreliable, maps sketchy and of little use. The country over which the men had to fly was wild and rough and sparsely populated, with few places for safe emergency landings.ASNL, Sep 3, 1919, pp 1–2.

Air Service squadrons flew along the border searching for bands of men and reported to the nearest cavalry post how many men they were, where they were, which way they were heading, what they were doing, and how many horses and cattle they had. The timing of the patrols varied so raiders would not know when the next plane would appear.Maj Henry H. Arnold, History of Rockwell Field (1923), p 87, MS in AFHRC 168.65041

Airfields

The patrol bases were hurriedly created. One of the young lieutenants who flew from Marfa Field in the summer of 1919 remembered the flying field as a pasture at the eastern edge of town. Its five hangars were made from canvas. A double row of ten or twelve tents served as officer and enlisted quarters and sheltered flight headquarters and supply. The lieutenant, Stacy C. Hinkle, recalled his tour of duty on the border as “a life of hardship, possible death, starvation pay, and a lonely life without social contacts, in hot, barren desert wastes, tortured by sun, wind, and sand.” The boredom was as bad as the physical hardship and discomfort, the sole recreation being drinking and gambling. Even so, Hinkle thought the airmen better off than the poor fellows at cavalry outposts up and down the border.

Primary airfields used in the Border Patrol mission were:

Calexico Field, California

Del Rio Field, Texas

Douglas Field, Arizona

Eagle Pass Field, Texas

El Centro Field, California

Fort Bliss, Texas

Kelly Field, Texas

March Field, California

Marfa Field, Texas

McAllen Field, Texas

Nogales Field, Arizona

Ream Field, California

Rockwell Field, California

Sanderson Field, Texas

Secondary airfields used on an as-needed bases, without garrisons, were at Bosque Bonite, Texas; Brownsville, Texas; Candelaria, Texas; Columbus Airfield, New Mexico; Fort Huachuca, Arizona; Lajitas, Texas; McAllen, Texas; Wellton, Arizona; Yuma, Arizona. and Zapata, Texas.

Border incidents

Pilots flying along or near the border were under orders not to cross. But they often got lost and strayed into Mexico. At times they went over deliberately, apparently on the spur of the moment. Occasionally, they crossed to carry out a special assignment.