Question: When was the American single-engined, single-seat, all-metal fighter and ground-attack aircraft first flew in which design Donovan Reese Berlin was associated?

Context paragraphs:
Curtiss P-40 Warhawk: The Curtiss P-40 Warhawk is an American single-engined, single-seat, all-metal fighter and ground-attack aircraft that first flew in 1938.  The P-40 design was a modification of the previous Curtiss P-36 Hawk which reduced development time and enabled a rapid entry into production and operational service.  The Warhawk was used by most Allied powers during World War II, and remained in frontline service until the end of the war.  It was the third most-produced American fighter, after the P-51 and P-47; by November 1944, when production of the P-40 ceased, 13,738 had been built, all at Curtiss-Wright Corporation's main production facilities at Buffalo, New York.

Don R. Berlin: Donovan Reese Berlin (June 13, 1898 – May 17, 1982) was an American military aircraft designer and aircraft industry executive.  Among the many designs with which he is associated, are the Curtiss P-36 Hawk, Curtiss P-40 Warhawk and Fisher P-75 Eagle.  His name is "synonymous with the development of military aviation".  He designed aircraft that were safe, rugged and "a pilot's joy."

Kawasaki Ki-64: The Kawasaki Ki-64 (Allied code name: Rob) was a one-off prototype of an experimental heavy, single seat, fighter.  It had two unusual design features.  First; it had two Kawasaki Ha-40 engines in tandem; one in the aircraft nose, the other behind the cockpit, both being connected by a drive shaft.  This combination (called the Kawasaki Ha-201) drove two, three-bladed, contra-rotating propellors.  The second feature was the use of the wing surface as a radiator for the water-cooled engines.  The aircraft first flew in December 1943.  During the fifth flight, the rear engine caught fire; and while the aircraft made an emergency landing, it was damaged.  The aircraft was subsequently abandoned in mid-1944 in favour of more promising projects.  The airframe survived the war, and parts of the unique cooling system were sent to Wright Field for examination.

Polikarpov I-5: The Polikarpov I-5 was a single-seat biplane which became the primary Soviet fighter between its introduction in 1931 through 1936, after which it became the standard advanced trainer.  Following Operation Barbarossa, which destroyed much of the Soviet Air Forces (VVS), surviving I-5s were equipped with four machine guns and bomb racks and pressed into service as light ground-attack aircraft and night bombers in 1941.  They were retired in early 1942 as Soviet aircraft production began to recover and modern ground-attack aircraft like the Ilyushin Il-2 became available.  A total of 803 built (including 3 prototypes).

Junkers D.I: The Junkers D.I (factory designation J 9) was a monoplane fighter aircraft produced in Germany late in World War I, significant for becoming the first all-metal fighter to enter service.  The prototype, a private venture by Junkers designated the J 7, first flew on 17 September 1917, going through nearly a half-dozen detail changes in its design during its tests.  When it was demonstrated to the "Idflieg" early the following year it proved impressive enough to result in an order for three additional aircraft for trials.  However, the changes made by Junkers were significant enough for the firm to redesignate the next example the J 9, which was supplied to the "Idflieg" instead of the three J 7s ordered.

IAR 80: The IAR 80 was a Romanian World War II low-wing monoplane, all-metal monocoque fighter and ground-attack aircraft.  When it first flew, in 1939, it was comparable to contemporary designs being deployed by the airforces of the most advanced military powers.  Production problems and lack of available armament delayed entry of the IAR 80 into service until 1941.  It remained in frontline use until May 1945.

Piper PA-8: The Piper PA-8 Skycycle was a 1940s American single-seat light aircraft designed and built by Piper Aircraft at their Lock Haven, Pennsylvania plant.  Towards the end of 1944 Piper announced a number of aircraft it intended to build after the war.  One of these was the PWA-8 (Post War Airplane 8).  An aerodynamic test aircraft was built with the name Cub Cycle and it first flew on 27 August 1944 with a small two cylinder Franklin engine.  The Franklin engine was replaced by a 37 hp Continental A-40-3 and the aircraft first flew with the Continental engine on 12 September 1944.  The Skycycle was a fabric-covered mid-wing single-engined single-seat monoplane with a tailwheel landing gear.  The fuselage was produced using a belly fuel tank as used on the F4U Corsair.  The Cub Cycle was scrapped and a similar but new aircraft was built with the name Skycycle.  The Skycycle first flew on 29 January 1945 using the same Continental engine as the Cub Cycle.  The aircraft was further modified in 1945 with a 55 hp Lycoming O-145-A2 engine and designated the PA-8 Skycycle.  No further examples were built.

Junkers CL.I: The Junkers CL.I was a ground-attack aircraft developed in Germany during World War I.  Its construction was undertaken by Junkers under the designation J 8 as proof of Hugo Junkers' belief in the monoplane, after his firm had been required by the "Idflieg" to submit a biplane (the J 4) as its entry in a competition to select a ground-attack aircraft.  The J 8 design took the J 7 fighter as its starting point, but had a longer fuselage to accommodate a tail gunner, and larger wings.  The prototype flew in late 1917 and was followed over the next few months by three more development aircraft.  The "Idflieg" was sufficiently impressed to want to order the type, but had misgivings about Junkers' ability to manufacture the aircraft in quantity and considered asking Linke-Hoffmann to produce the type under licence.  Finally, however, Junkers was allowed to undertake the manufacture as part of a joint venture with Fokker, producing a slightly modified version of the J 8 design as the J 10.  Like the other Junkers designs of the period, the aircraft featured a metal framework that was skinned with corrugated duralumin sheets.  47 examples were delivered before the Armistice, including three built as floatplanes under the designation CLS.I (factory designation J 11).  After the war, one or two CL.Is were converted for commercial service by enclosing the rear cockpit under a canopy.

Renard R.36: The Renard R.36 was a Belgian all-metal fighter aircraft designed to replace the Fairey Firefly II within the Belgian Air Force.  Designed to improve on the Renard Epervier, which was never adopted by the Belgian government, the prototype R.36 first flew on 5 November 1937.  Following testing the R.36 was approved by the Belgian Air Force in late 1938, with 40 aircraft provisionally ordered, to be delivered in two years.  However, on 17 January 1939 the prototype, "OO-ARW", crashed near Nivelles, killing pilot Lt. Viscount Eric de Spoelberch.  The official investigation was inconclusive, no evidence of material failure being discovered, with the most probable causes being radio equipment coming loose during a high-G manoeuver, jamming the controls, or the pilot becoming incapacitated.  The airframe had accumulated 75:30 hours flight time.  The order was then dropped in favour of licence production of the Hawker Hurricane by SABCA.

Sopwith Salamander: The Sopwith TF.2 Salamander was a British ground-attack aircraft of the First World War designed by the Sopwith Aviation Company which first flew in April 1918.  It was a single-engined, single-seat biplane based on the Sopwith Snipe fighter but with an armoured forward fuselage to protect the pilot and fuel system from ground fire during low level operations.

Supporting paragraphs: Don R. Berlin Curtiss P-40 Warhawk
Answer: 1938