The 1917 French twin-engine Caudron G.4 has great significance as an early light bomber and reconnaissance aircraft. It was a principal type used when these critical air power missions were being conceived and pioneered in World War I. Although fighter aircraft frequently gain greater attention, the most influential role of aviation in the First World War was reconnaissance. The extensive deployment of the Caudron G.4 in this role makes it an especially important early military aircraft. Moreover, despite its speed and armament limitations, the Caudron G.4 was quite reliable, had a good rate of climb, and was pleasant to fly, all characteristics that made it a good training aircraft after its combat effectiveness was reduced. Many Allied pilots received their initial flight training on the Caudron G.4. The NASM Caudron is among the oldest surviving bomber aircraft in the world, and one of the very few remaining multi-engine aircraft from this period.

Gaston and René Caudron were among the earliest aircraft manufacturers in France. After building and testing a few original designs in 1909 and early in 1910, the brothers established a flight training school at Crotoy and an aircraft factory at Rue in 1910. The first factory-produced Caudron was the type A4, a 35-horsepower Anzani-powered tractor biplane in which the pilot sat completely exposed behind the rear spar of the lower wing. The next major Caudron design, the type B, was the first to feature the abbreviated fuselage/pilot nacelle, characteristic of many later Caudron aircraft. It was powered by a 70-horsepower Gnôme or 60-horsepower Anzani engine mounted in the front of the nacelle with the pilot immediately behind. Although a tractor, the tail unit of the type B was supported by booms extending from the trailing edge of the wings, an arrangement more commonly featured on pusher aircraft. Lateral control was accomplished with wing warping. The type B established the basic configuration of Caudron designs through the G.4 model.

The first of the well-known Caudron G series aircraft appeared in 1912. Initially designed as a trainer, the type G was developed into the G.2 by the outbreak of the First World War, and saw limited military service in 1914 as single and two-seat versions. By that time the Caudron factory had been relocated to Lyon, where an improved version, designated the G.3, was being produced in significant numbers. Soon a second factory was opened at Issy-les-Moulineaux, near Paris, to meet military demand for the airplane. The G.3 was primarily a two-seat aircraft, but a few were converted to single-seat versions. They were powered variously by 80-horsepower Le Rhône or Gnôme rotary engines or a 90-horsepower Anzani radial. A total of 2,450 G.3s were built, including a small number built under license in Britain and Italy.

The Caudron G.4 was a larger, twin-engined version of the G.3, powered by two 80-horsepower Le Rhônes or 100-horsepower Anzanis. The Anzani-powered Caudron G.4s served mostly as training aircraft. Some of the Anzani-powered G.4s, but not all, had their engines set up to turn in opposite directions to balance the torque of the whirling propellers. All the Le Rhône-powered Caudrons had both engines rotating in the same direction, clockwise from the pilot's orientation. Also, the two vertical tail surfaces of the G.3 were increased to four on the G.4. The twin-engined configuration increased the range of the Caudron and provided a location for a forward-firing machine gun, typically a Hotchkiss or Lewis, although other types were also used. To protect against attacks from behind, some G.4s were fitted with an additional gun mounted on the top of the upper wing and pointed rearward, but this proved to be ineffective and it was frequently removed from operational aircraft. A number of G.4s had a second gun mounted immediately in front of the pilot on the deck of the nacelle (such as on the NASM Caudron). But more often the pilot and observer simply carried hand-held weapons to respond to attacks from the rear. Some G.4s carried a camera for high-altitude reconnaissance.

The prototype G.4 first flew in March 1915, and 1,358 were built in three major versions: the Caudron G.4A2 for reconnaissance, the G.4B2 for bombing, and the G.4E2 for training. The A2 had a wireless set for artillery spotting missions; the B2 could carry up to 100 kg (220 lb) of bombs; and the E2 had dual controls for instruction. A special armored version of the G.4, designated the G.4IB, was deployed to the top French units, the "B" representing Blindage, the French word for armor. In addition to reconnaissance, bombing, and training, the Caudron G.4 also sometimes served as a long-range escort to other bomber aircraft.

By 1916, the G.4 was replacing the G.3 in most Caudron squadrons. Extensively used as a bomber during the first half of 1916, its deployment in that role was severely reduced by the fall of that year. The Caudron's relative slow speed and inability to defend itself from the rear made it increasingly vulnerable to fighter attack as German air defense improved. But Caudrons continued to be widely used as reconnaissance aircraft well into 1917. By early 1918 virtually all Caudron aircraft still in use were relegated to training duties. In addition to the French, Caudrons were used extensively by British and Italian units, and a few were used by the Russians and the Belgians. Ten Caudron G.4s were sold to the United States in November 1917 and transferred to the U.S. Air Service's 2nd Air Instruction Center at Tours. Used exclusively as trainers, none of these Caudrons saw operational service with American units.

The Caudron G.4 was in many respects a pre-war design, with its wing-warping lateral control, light structure, and limited visibility. Yet it has great significance as an early light bomber and reconnaissance aircraft. It was a principal type used when these critical air power missions were being conceived and pioneered in World War I. Although fighter aircraft frequently gain greater attention, the most influential role of aviation in the First World War was reconnaissance. The extensive deployment of the Caudron in this role make it an especially important early military aircraft. Moreover, despite its speed and armament limitations, the Caudron was quite reliable, had a good rate of climb, and was pleasant to fly, all characteristics that made it a good training aircraft after its combat effectiveness was reduced. Many Allied pilots received their initial flight training on the Caudron. For all these reasons the Caudron occupies an important place in aviation history and in the National Air and Space Museum's aircraft collection. As an individual museum specimen, the NASM Caudron G.4 also has great significance. It is among the oldest surviving bomber aircraft in the world. Further, it is the only very early multi-engine airplane in the NASM collection, and one of the very few multi-engine aircraft from this period anywhere.

The Caudron G.4 in the NASM collection, serial # C4263, was built by the Eugene firm and left the factory on December 12, 1916. The marking "12_16" appears on the leading edge of each individual wing section and some other major components of the aircraft, confirming the manufacturing date acquired from archival sources. Its acceptance flight was made at Issy-les-Moulineaux on December 27, 1916. The pilot's name was Gerviès and it was reported that the airplane climbed to 1000 m (3,281 ft) in 7 minutes. The airplane had full radio and photographic equipment, characterized by the A2 reconnaissance variant. Caudron G.4 serial # C4263 saw no operational activity with the French Air Service. It was apparently sent to the Reserve Générale of the Aviation Militaire and remained there until it was purchased by the United States government in early 1917 through the American Ambassador, Mr. Sharp. The Caudron was acquired, along with a Voisin Type 8 (also in the NASM collection) and a Farman aircraft, for technical evaluation by the United States. However, by the time the aircraft were transported to the U.S. and prepared for flight demonstrations, they were already outmoded. This airplane was not among the ten purchased late in 1917 and deployed as trainers. Photographic evidence demonstrates that the NASM Caudron had arrived in the U.S. and was at Langley Field, Hampton, Virginia, at least by July 26, 1917, four months before the contract for the ten training aircraft was executed.

In a 1966 article in the journal Cross & Cockade on the NASM Caudron, the author, Brian Flanagan, states that at some point before the end of the war, "the Caudron and the Voisin were exhibited in a park in Washington, D.C., as part of a war drive display." But he cites no source for this fact.

On July 12, 1918, Lt. Col. L.S. Horner, of the War Department's Bureau of Aircraft Production, wrote to Smithsonian Institution Secretary, Charles Walcott, regarding "obsolete airplanes for exhibition purposes," offering the Caudron, the Voisin, and the Farman aircraft to the Institution. The offer was accepted and the three airplanes were delivered to the museum on September 16 and 17, 1918. The Farman was very incomplete and was deemed unacceptable for exhibition. It was returned to the War Department in June 1921. Because of an oversight when packing the Farman for shipment, its wings remained at the Smithsonian until September 1925, when they were either returned to the War Department or destroyed. The record is unclear.

The Caudron was delivered to the Smithsonian without engines, propellers, or armament. It was soon assembled and suspended in the Arts and Industries building, lacking these components. In 1929, Paul Garber, of the Smithsonian curatorial staff, acquired engines and propellers from the War Department, and had them installed on the Caudron. Unfortunately, Garber was unable to obtain the proper 80-horsepower Le Rhône rotary engines. Only 110-horsepower Le Rhônes were available, and Garber considered these to be at least representative of the correct powerplants. Similarly, the propellers acquired and installed on the airplane were only representative of the period and not the precise type that were actually used on the Caudron. Internal parts of the 110-horsepower Le Rhônes, such as pistons, connecting rods, etc., were removed from the engines to lighten them and put in storage. Smithsonian officials took this action as a safety measure because the airplane was suspended over a public area. The Caudron was displayed in this manner until the late 1960s or early 1970s, when it was removed from the Arts and Industries building and placed in storage at the Garber Facility. It received preservation treatment in 2000. Also at that time, the incorrect 110-horsepower Le Rhône rotary engines were replaced with the proper 80-horsepower Le Rhônes, and correct propellers were fabricated.

One interesting marking on the tail of the NASM Caudron is the term "Blindage 16K" on the rudders. Blindage is the French word for armored, indicating that the museum's airplane could be one of the special G.4IB armored Caudrons. The armor consisted of a heavy metal plate inserted behind the seat of the rear cockpit, protruding upward so as to cover the back and head of the pilot. The armor plate is missing on the NASM Caudron. However, there is a gap, or slot, in the structure immediately behind the seat where such a plate would fit. Photographs of other Caudrons with the armor plate inserted show it in the same location as the slot behind the rear seat on the NASM Caudron. This, along with the marking "Blindage 16 K," strongly indicate that the NASM airplane was an armored version of the Caudron G.4.