Hugo Junkers' experimental all-metal aircraft never received an official "A" nor an "E-series" monoplane designation because it was primarily intended as a practical demonstration of Junkers' metal-based structural ideas, and was officially only known by its Junkers factory model number of J 1.
In July 1915 the Junkers firm got its first aircraft construction contract from the German government, the design of what would become the Junkers J 1 and by November 1915, the completed J 1 was ready for initial testing.
The Junkers J 1 was a mid-wing monoplane with a cantilever wing, without exterior bracing struts or wires. External bracing was only used for support of the horizontal stabilizer and the undercarriage.
The fuselage used welded strip-steel angle stock and I-beam sections along with some steel tubing to form its main internal structure with 17 in wide sheet steel panels wrapped around the fuselage to form its covering.
The single vertical tail surface was of an "all-flying" design (with no fixed fin) and the entire tail surface structure and covering also consisted of formed and sheet steel, much like the wings.
The 90 kW (120 hp) Mercedes D.II six-cylinder liquid-cooled inline engine selected for the design had a simple, clamshell-like horizontally split cowling enclosing the engine's crankcase and lower cylinder block, and an advanced engine radiator layout.
Flight testing began on 12 December and would continue into January. After minor adjustments the in-flight handling of the J 1 was deemed acceptable and it was stable in flight. On 19 January, the J 1 flew it’s only known "high performance" flight test, which consisted of a 4.3 mi course, at varying altitudes from 660–980 ft, and managed a top speed of 110 mph. The Junkers J 1 was probably not flown again after January 1916.
The J 1 was compared to the popular Rumpler C.I two-seat armed observation biplane, which was some 19 mph slower in its top speed, even though the Rumpler biplane had the more powerful Mercedes D.III engine, but due to the lighter weight of the Rumpler's wood-and-fabric structure it had a much better climb rate than the J 1 with its experimental steel structure.
Nonetheless, Junkers was given a contract to further develop his all-metal concept which would become the basis for today’s modern aircraft.