9 September 1940: North American Aviation completed assembly of the NA-73X, the first prototype of the new Mustang Mk.I fighter for the Royal Air Force. This was just 117 days after the British Purchasing Commission had authorized the construction of the prototype. The airplane was designed by a team led by Edgar Schmued. The 1,150-horsepower Allison V-12 engine had not yet arrived, so the NA-73X was photographed with dummy exhaust stacks. The prototype’s company serial number was 73-3097. It had been assigned a civil experimental registration number, NX19998.
The NA-73X was a single-seat, single-engine, low wing monoplane with retractable landing gear. It was primarily of metal construction, though the flight control surfaces were fabric covered. The airplane was designed for the maximum reduction in aerodynamic drag. The Mustang was the first airplane to use a laminar-flow wing. The fuselage panels were precisely designed and very smooth. Flush riveting was used. The coolant radiator with its intake and exhaust ducts was located behind and below the cockpit. As cooling air passed through the radiator it was heated and expanded, so that as it exited, it actually produced some thrust.
The prototype was 32 feet, 2⅝ inches (9.820 meters) long, with a wing span of 37 feet, 5/16 inch (11.286 meters). Empty weight of the NA-73X was 6,278 pounds (2,848 kilograms) and normal takeoff weight was 7,965 pounds (3,613 kilograms).
The NA-73X was powered by a liquid-cooled, supercharged, 1,710.60-cubic-inch-displacement (28.032 liter) Allison Engineering Company V-1710-F3R (V-1710-39) single overhead cam 60° V-12 engine, with four valves per cylinder and a compression ratio of 6.65:1. It used a single-stage, single-speed supercharger. This was a right-hand tractor engine (the V-1710 was built in both right-hand and left-hand configurations) which drove a 10 foot, 6 inch (3.200 meter) diameter, three-bladed, Curtiss Electric constant-speed propeller through a 2.00:1 gear reduction.
The V-1710-39 had a Normal Power rating of 880 horsepower at 2,600 r.p.m. at Sea Level; Take Off Power rating of 1,150 horsepower at 3,000 r.p.m. at Sea Level, with 44.5 inches of manifold pressure (1.51 Bar), 5 minute limit; and a War Emergency Power rating of 1,490 horsepower at 3,000 r.p.m., with 56 inches of manifold pressure (1.90 Bar). The V-1710-F3R was 7 feet, 4.38 inches (2.245 meters) long, 3 feet, 0.64 inches (0.931 meters) high, and 2 feet, 5.29 inches (0.744 meters) wide. It had a dry weight of 1,310 pounds (594 kilograms).
U.S. Army Air Corps flight tests of the fully-armed production Mustang Mk.I (XP-51 41-038), equipped with the V-1710-39 and a 10 foot, 9-inch (3.277 meters) diameter Curtiss Electric propeller, resulted in a maximum speed of 382.0 miles per hour (614.8 kilometers per hour) at 13,000 feet (3,962 meters). The service ceiling was 30,800 feet (9,388 meters) and the absolute ceiling was 31,900 feet (9,723 meters).
The Curtiss P-40D Warhawk used the same Allison V-1710-39 engine as the XP-51, as well as a three-bladed Curtiss Electric propeller. During performance testing at Wright Field, a P-40D, Air Corps serial number 40-362, weighing 7,740 pounds (3,511 kilograms), reached a maximum speed of 354 miles per hour (570 kilometers per hour) at 15,175 feet (4,625 meters). Although the Mustang’s test weight was 194 pounds (88 kilograms) heavier, at 7,934 pounds (3,599 kilograms), the Mustang was 28 miles per hour (45 kilometers per hour) faster than the Warhawk. This demonstrates the effectiveness of the Mustang’s exceptionally clean design.
Only one NA-73X was built. It made its first flight 26 October 1940 with test pilot Vance Breese. The prototype suffered significant damage when it overturned during a forced landing, 20 November 1941. NX19998 was repaired and flight testing resumed. The prototype’s final disposition is not known.
Originally ordered by Great Britain, the Mustang became the legendary U.S. Army Air Corps P-51 Mustang. A total of 15,486 Mustangs were built by North American Aviation at Inglewood, California and Dallas, Texas. Another 200 were built in Australia by the Commonwealth Aircraft Corporation.
The P-51 remained in service with the U.S. Air Force until 27 January 1957 when the last one, F-51D-30-NA 44-74936, was retired from the 167th Fighter Squadron, West Virginia Air National Guard. It was then transferred to the National Museum of the United States Air Force at Wright-Patterson Air Force Base, where it is on display.
24 August 1942: Flying a Grumman F4F Wildcat, Lieutenant Marion Eugene Carl, United States Marine Corps, a 27-year-old fighter pilot assigned to Marine Fighter Squadron 223 (VMF-223) based at Henderson Field, Guadalcanal Island, shot down four enemy airplanes in one day. They were a Mitsubishi A6M “Zeke” fighter, a Mitsubishi G4M1 “Betty” medium bomber and two Nakajima B5N2 “Kate” torpedo bombers. Carl had previously shot down an A6M during the Battle of Midway, less than three months earlier. He now had five aerial combat victories, making him the Marine Corps’ first ace.
Captain Carl was awarded the Navy Cross (his second) for his actions in the Solomon Islands from 24 August to 9 September 1942.
Marion Carl’s fighter was a Grumman F4F-4 Wildcat, designed by Robert Leicester Hall as a carrier-based fighter for the United States Navy. The F4F-4 was a single-place, single-engine, mid-wing monoplane with retractable landing gear.
The F4F-4 was 29 feet, 9-3/8 inches (9.077 meters) long, with a wingspan of 38 feet, 0 inches (11.582 meters) and overall height of 12 feet, 1-3/8 inches (3.693 meters). Unlike the preceding F4F-3, the F4F-4 had folding wings for storage aboard aircraft carriers. With the wings folded, the airplane was 14 feet, 4 inches (4.369 meters) wide. Its empty weight was 5,895 pounds (2,674 kilograms), and the gross weight was 7,975 pounds (3,617 kilograms).
The F4F-4 was powered by an air-cooled, supercharged, 1,829.39-cubic-inch-displacement (29.978 liter) Pratt & Whitney Twin Wasp SSC7-G (R-1830-86) two-row, 14-cylinder radial engine with a compression ratio of 6.7:1. The R-1830-86 had a normal power rating of 1,100 at 2,550 r.p.m., from Sea Level to 3,300 feet (1,006 meters), and 1,000 horsepower at 2,550 r.p.m. at 19,000 feet (5,791 meters). It was rated at 1,200 horsepower at 2,700 r.p.m. for takeoff. The engine turned a three-bladed Curtiss Electric propeller with a diameter of 9 feet, 9 inches (2.972 meters) through a 3:2 gear reduction. The R-1830-86 was 4 feet, 0.19 inches (1.224 meters) in diameter, 5 feet, 7.44 inches (1.713 meters) long, and weighed 1,560 pounds (708 kilograms).
The F4F-4 had a maximum speed of 284 miles per hour (457 kilometers per hour) at Sea Level, and 320 miles per hour (515 kilometers per hour) at 18,800 feet (5,730 meters). Its service ceiling was 34,000 feet (10,363 meters).
While the F4F-3 Wildcat was armed with four air-cooled Browning AN-M2 .50-caliber machine guns; the F4F-4 had six. It carried 1,400 rounds of ammunition.
The prototype XF4F-1 made its first flight in 1935. It was substantially improved as the XF4F-2. The first production F4F-3 Wildcat was built in February 1940. The airplane remained in production through World War II, with 7,860 built by Grumman and General Motors Eastern Aircraft Division (FM-1 Wildcat).
According to the National Naval Aviation Museum, F4F Wildcats held a 9:1 ratio of victories over Japanese aircraft, with 1,006 enemy airplanes destroyed in combat.
Marion Eugene Carl was born at Hubbard, Oregon, 1 November 1915. He was the second of four children of Herman Lee Carl, a dairy farmer, and Ellen Lavine Ellingsen Carl.
Carl graduated from Oregon State College at Corvallis, Oregon, and was commissioned as a second lieutenant in the United States Army Reserve, 31 May 1938. Lieutenant Carl soon resigned this commission to accept an appointment as an Aviation Cadet, United States Navy. He enlisted as a private, first class, Volunteer Marine Corps Reserve, 17 July 1938, and was designated a student Enlisted Naval Aviation Pilot assigned to the Naval Reserve Aviation Base, Squantum, Massachusetts. He entered flight school as an Aviation Cadet at Naval Air Station Pensacola near Pensacola, Florida, 26 July 1938.
After completing flight training, Carl was commissioned as a Second Lieutenant, United States Marine Corps Reserve, 20 October 1939. He was then assigned to Marine Fighting Squadron One (VMF-1) at Brown Field, Quantico, Virginia.
In 1940, Lieutenant Carl returned to NAS Pensacola as a flight instructor. On 25 February 1941, Second Lieutenant Carl, U.S.M.C.R., was appointed a Second Lieutenant, United States Marine Corps.
Lieutenant Carl was transferred to VMF-221 at San Diego, California, as a fighter pilot. The unit was assigned to the aircraft carrier USS Saratoga (CV-3) for transportation to Marine Corps Air Station Ewa, Oahu, Territory of Hawaii. On 25 December 1941, VMF-221 was deployed to Midway Atoll.
Marion Carl and his squadron fought during the Battle of Midway. Flying a Grumman F4F-3 Wildcat, Bu. No. 1864,¹ on 4 June 1942, he shot down his first enemy airplane, a Mitsubishi A6M Zero fighter, and damaged two others. Lieutenant Carl was awarded the Navy Cross for his actions in that decisive battle.
Marion Carl was next assigned to VMF-223 under the command of Captain John L. Smith. The Marine fighter squadron was the first air unit to arrive at Henderson Field on the island of Guadalcanal in the Solomons, 20 August 1942. This was a critical airfield, originally built by the Japanese military but occupied by Allied forces. On 24 August, Lieutenant Carl became the Marine Corps’ first “ace.”
Carl was shot down in 9 September 1942 and was missing for five days. He was helped by islanders who eventually returned him to his base.
The squadron departed Guadalcanal 16 October 1942, and sailed to San Francisco, California. VMF-223 was credited with destroying 110½ enemy aircraft. Carl was credited with 16.
Lieutenant Carl married Miss Edna T. Kirvin at New York City, New York, 7 January 1943.
On 26 January, he took command of VMF-223. On 8 May 1943, Lieutenant Carl was promoted to the temporary rank of captain. The squadron was re-equipped with the new Vought-Sikorsky F4U-1 Corsair. Training in the new fighter took place at MCAS El Toro, in southern California.
In August, the squadron returned to combat in the Solomons. By the end of 1943, Major Carl’s total of enemy aircraft destroyed was 18½ with 3 damaged, making him the seventh highest-scoring Marine fighter pilot of World War II.
After the War Marion Carl was assigned as a test pilot at NAS Patuxent River, Maryland, testing jet aircraft on aircraft carriers. He was also the first Marine Corps pilot to fly a helicopter. Carl commanded the Marine’s first jet squadron, VMF-122, which flew the McDonnell FH-1 Phantom. He was promoted to lieutenant colonel 7 August 1947.
In May 1955, Colonel Carl commanded Marine Photo Reconnaissance Squadron One (VMJ-1). The squadron flew the McDonnell FH-2 Banshee from air bases on the island of Formosa (Taiwan) on secret missions over the People’s Republic of China.
At Muroc Army Air Field (now Edwards Air Force Base) Marion Carl tested the Douglas D-558-I Skystreak and D-558-II Skyrocket, setting world records for speed and altitude. He was promoted to colonel, 1 October 1956.
By 1962 Colonel Carl was Director of Marine Corps Aviation. He was promoted to brigadier general, 1 June 1964. He commanded the First Marine Brigade during the Vietnam War and flew combat missions in jet fighters and helicopter gun ships.
Carl was promoted to major general in August 1967, with his date of rank retroactive to 1 June 1964. Carl commanded the 2nd Marine Aircraft Wing, then served as Inspector General of the Marine Corps from 1970 until 1973. When he retired in 1973, General Carl had accumulated more that 13,000 flight hours.
During his military career, Major General Carl was awarded the Navy Cross with two gold stars (three awards); The Legion of Merit with valor device and three gold stars (four awards); The Distinguished Flying Cross with four gold stars (five awards); and the Air Medal with two gold and two silver stars (twelve awards).
Tragically, General Carl was murdered in Roseburg, Oregon, 28 June 1998, as he defended his wife, Edna, during a home-invasion robbery. Mrs. Carl was wounded, but survived.
Major General Marion E. Carl, United States Marine Corps, is buried at Arlington National Cemetery.
¹ The fighter flown by Marion Carl to shoot down his first enemy airplane is often cited as Grumman F4F-3 Bu. No. 4000 (second bureau number series, 1935–1940). However, the entry in Carl’s certified pilot logbook for 4 June 1942 states the airplane he flew was F4F-3 Bu. No. 1864.
6 August 1945: At 0245 hours, a four-engine, long range heavy bomber of the 509th Composite Group, United States Army Air Forces, took off from North Field on the island of Tinian in the Northern Mariana Islands, on the most secret combat mission of World War II.
The Martin-Omaha B-29-45-MO Superfortress, 44-86292, under the command of Colonel Paul W. Tibbets, Jr., was carrying Bomb Unit L-11, the first nuclear weapon to be used during war. This was a 9,700-pound (4,400 kilogram) “gun type” fission bomb, the Mark I, code-named Little Boy. It contained 64 kilograms (141.1 pounds) of highly-enriched uranium. The bomb was 120 inches (3.048 meters) long with a diameter of 28 inches (0.711 meter). Although it was a very inefficient weapon, it was considered to be such reliable design that it had not been tested.
On the morning before the mission, Colonel Tibbets had his mother’s name painted on the nose of the airplane: Enola Gay. He had personally selected this bomber, serial number 44-86292, while it was still on the assembly line at the Glenn L. Martin Company plant at Bellevue, Nebraska, 9 May 1945. The B-29 was accepted by the Army Air Corps on 15 May and flown to the 509th’s base at Wendover, Utah, by Captain Robert A. Lewis, a B-29 aircraft commander who would act as Tibbets’ co-pilot on the atomic bombing mission.
The B-29 Superfortress was designed by the Boeing Airplane Company as its Model 345. Produced in three major version, the B-29, B-29A and B-29B, it was built by Boeing at Wichita, Kansas and Redmond, Washington; by the Bell Aircraft Corporation at Marietta, Georgia; and the Glenn L. Martin Company at Fort Crook (now Offutt Air Force Base, Omaha, Nebraska. A total of 3,943 Superfortresses were built.
The B-29 was the most technologically advanced airplane built up to that time, and required an immense effort by American industry to produce.
The B-29 Superfortress was 99 feet, 0 inches (30.175 meters) long with a wingspan of 141 feet, 3 inches (43.053 meters) and an overall height of 27 feet, 9 inches (8.458 meters). The standard B-29 had an empty weight of 74,500 pounds (33,793 kilograms) and gross weight of 120,000 pounds (54.431 kilograms).
The Silverplate B-29s differed from the standard production bombers in many ways. They were approximately 6,000 pounds (2,722 kilograms) lighter. The bomber carried no armor. Additional fuel tanks were installed in the rear bomb bay. The bomb bay doors were operated by quick-acting pneumatic systems. The bomb release mechanism in the forward bomb bay was replaced by a single-point release as was used in special British Lancaster bombers. A weaponeer’s control station was added to the cockpit to monitor the special bomb systems.
Enola Gay had four air-cooled, supercharged, 3,347.662-cubic-inch-displacement (54.858 liter) Wright Aeronautical Division R-3350-41 (Cyclone 18 787C18BA3) two-row 18-cylinder radial engines with direct fuel injection. The R-3350-41 had a compression ratio of 6.85:1 and required 100/130 aviation gasoline. It was rated at 2,000 horsepower at 2,400 r.p.m. at Sea Level, and 2,200 horsepower at 2,800 r.p.m, for take-off. The engines drove four-bladed Curtiss Electric reversible-pitch propellers with a diameter of 16 feet, 8 inches (5.080 meters), through a 0.35:1 gear reduction. The R-3350-41 was 6 feet, 2.26 inches (1.937 meters) long, 4 feet, 7.78 inches (1.417 meters) in diameter and weighed 2,725 pounds (1,236 kilograms).
With the exception of the tail gunner’s position, all defensive armament—four powered remotely operated gun turrets with ten .50-caliber machine guns—were deleted. Their remote sighting positions were also removed. Enola Gay carried 1,000 rounds of ammunition for each of the two remaining Browning AN-M2 .50-caliber machine guns in the tail.
With these changes, the Silverplate B-29s could fly higher and faster than a standard B-29, and the new engines were more reliable. Enola Gay had a cruising speed of 220 miles per hour (354 kilometers per hour) and a maximum speed of 365 miles per hour (587 kilometers per hour). Its service ceiling was 31,850 feet (9,708 meters) and its combat radius was 2,900 miles (4,667 kilometers).
At 09:15:17 a.m., (mission time, 8:15 a.m., local), Enola Gay was at 31,000 feet (9,450 meters) over the Japanese city of Hiroshima on the island of Honshu, an industrial center with a population of about 340,000 people. The bombardier initiated the automatic release sequence and the the atomic bomb was dropped. It fell for 44.4 seconds and detonated at an altitude of 1,968 feet (600 meters), about 800 feet (244 meters) from the aiming point, the Aioi Bridge over the Ota River.
Ground Zero, the point on the surface directly below the explosion, was the Shima Hospital. The overpressure is estimated to have been 4.5–6.7 tons per square meter. The two-story brick building was completely obliterated. Of the patients, technicians, nurses and doctors inside, nothing remained.
The resulting explosion was approximately equivalent in explosive force to the detonation of 16,000 tons (14,515 metric tons) of TNT (16 “kilotons”). An estimated 70,000 people were killed immediately, and another 70,000 were wounded. As many as 160,000 people may have died as a result of the atomic bombing by the end of 1945. More would follow over the next few years.
An area of the city with a radius of 1 mile (1.6 kilometers) from the point of detonation (“hypocenter”) was totally destroyed, and combined with the fires that followed, 4.7 square miles (12.17 kilometers²) of the city were destroyed. 69% of all buildings in Hiroshima were completely destroyed and another 6% damaged.
As soon as the bomb was released, Colonel Tibbets turned his B-29 away to avoid the blast. It was just over 11 miles (17.7 kilometers) from the detonation point when the shock waves hit, but no damage resulted. The bomber was then flown back to Tinian, landing after an elapsed time of 12 hours, 13 minutes.
Enola Gay was placed in storage at Davis-Monthan Army Air Field, Tucson, Arizona, 26 July 1946, and was transferred to the Smithsonian Institution just over one month later, 30 August 1946. For decades it sat in storage at different locations around the country, but finally a total restoration was performed. Today, the B-29 is on display at the Steven F. Udvar-Hazy Center, National Air and Space Museum.
6 May 1941: Just eight months after a prototype for a new single-engine fighter was ordered by the U.S. Army Air Forces, test pilot Lowery Lawson Brabham took off from the Republic Aviation Corporation factory airfield at Farmingdale, New York, and flew the prototype XP-47B Thunderbolt, serial number 40-3051, to Mitchel Field, New York.
During the flight, oil which had collected in the exhaust duct began burning. There was so much smoke that Brabham considered bailing out. He stayed with the prototype, though, and when he arrived at Mitchel Field, he exclaimed, “I think we’ve hit the jackpot!”
The prototype was designed by Alexander Kartveli, a Georgian immigrant and former chief engineer for the Seversky Aircraft Corporation, which became the Republic Aviation Corporation in 1939.
Alexander Kartveli (née Kartvelishvili, ალექსანდრე ქართველი) was born in Tbilisi, in the Kutais Governorate of the Russian Empire, (what is now, Georgia). After World War I, during which he was wounded, Kartvelishvili was sent to study at the Paris Aviation Higher College of Engineering in France by the government of the Democratic Republic of Georgia. He graduated in 1922. Kartvelishvili did not return to his country, which had fallen to the Red Army in the Soviet-Georgian War. He worked for Blériot Aéronautique S.A. until 1928, when he was employed by the Fokker American Company (also known as Atlantic Aircraft, or Atlantic-Fokker) which was headquartered at Passaic, New Jersey, in the United States. In 1931, he became chief engineer for the Seversky Aircraft Company in Farmingdale.
The XP-47B was the largest single-engine fighter that had yet been built. The production P-47B was 34 feet, 10 inches (10.617 meters) long with a wingspan of 40 feet, 9-5/16 inches (12.429 meters), and height of 12 feet, 8 inches (3.861 meters).¹ The wing area was 300 square feet (27.9 square meters). At a gross weight of 12,086 pounds (5,482 kilograms), it was nearly twice as heavy as any of its contemporaries.
The XP-47B was powered by an air-cooled, supercharged and turbocharged, 2,804.4-cubic-inch-displacement (45.956 liter) Pratt & Whitney R-2800-21 (Double Wasp TSB1-G) two-row, 18-cylinder radial with a compression ratio of 6.65:1 had a normal power rating of 1,625 horsepower at 2,550 r.p.m., to an altitude of 25,000 feet (7,620 meters), and a takeoff/military power rating of 2,000 horsepower at 2,700 r.p.m. at 25,000 feet (7,620 meters). The engine drove a 12-foot, 2 inch (3.708 meter) diameter, four-bladed Curtiss Electric constant-speed propeller through a 2:1 gear reduction. The R-2800-21 was 4 feet, 4.50 inches (1.340 meters) in diameter and 6 feet, 3.72 inches (1.923 meters) long. The engine weighed 2,265 pounds (1,027 kilograms). Approximately 80% of these engines were produced by the Ford Motor Company. It was also used as a commercial aircraft engine, with optional propeller gear reduction ratios.
A large General Electric turbosupercharger was mounted in the rear of the fuselage. Internal ducts carried exhaust gases from the engine to drive the turbocharger. This supercharged air was then carried forward through an intercooler and then on to the carburetor to supply the engine. The engine’s mechanical supercharger further pressurized the air-fuel charge.
During flight testing, the XP-47B Thunderbolt demonstrated speeds of 344.5 miles per hour (554.4 kilometers per hour) at 5,425 feet (1,654 meters), and 382 miles per hour (615 kilometers per hour) at 15,600 feet (4,745 meters). Its maximum speed was 412 miles per hour (663 kilometers per hour) at 25,800 feet (7,864 meters). The test pilot reported that the engine was unable to produce full power during these tests. It was determined that it had a cracked cylinder head, resulting in a loss of 2.5–4% of its maximum rated power. Also, the XP-47B was painted in camouflage, resulting in a slight loss of speed.
It could climb to 15,000 feet (4,572 meters) in just five minutes.
The Thunderbolt was armed with eight Browning AN-M2 .50-caliber machine guns, four in each wing, with 3,400 rounds of ammunition. It could also carry external fuel tanks, rockets and bombs. The structure of the P-47 could be described as “robust” and it was heavily armored. The amount of damage that the airplane could absorb and still return was remarkable.
During a test flight, 4 August 1942, the XP-47B’s tail wheel was left down. The extreme heat of the turbocharger’s exhaust set fire to the tire, which then spread to the airplane’s fabric-covered control surfaces. Unable to control the airplane, test pilot Filmore L. Gilmer bailed out. The prototype Thunderbolt crashed into Long Island Sound and was destroyed.
A total of 15,683 Thunderbolts were built; more than any other Allied fighter type. In aerial combat, it had a kill-to-loss ratio of 4.6:1. The P-47, though, really made its name as a ground attack fighter, destroying aircraft, locomotives, rail cars, and tanks by the many thousands. It was one of the most successful aircraft of World War II.
¹ Data from Pilot’s Flight Operating Instructions, Technical Order No. 01-65BC-1, 20 January 1943
6 May 1935: At Buffalo, New York, the prototype Curtiss-Wright Model 75, NX17Y, serial number 11923, made its first flight.
Designed by Donovan Reese Berlin, the airplane was a modern design of all metal construction, with fabric covered control surfaces. The Model 75 was a single-seat, single-engine low wing monoplane with retractable landing gear.
In its original configuration, the Model 75 was powered by an air-cooled, supercharged 1,666.860 cubic inch displacement (27.315 liter) Wright Aeronautical Division GR1670A1 two-row 14-cylinder radial engine. The GR1670A1 was a developmental engine with a compression ratio of 6.75:1. It was rated at 775 horsepower at 2,400 r.p.m. at Sea Level, and 830 horsepower at 2,600 horsepower for takeoff, burning 87-octane gasoline. The engine was 3 feet, 9 inches (1.143 meters) in diameter, 4 feet, 4–25/32 inches (1.341 meters) long, and weighed 1,160 pounds (526 kilograms). The GR1670A1 drove a three-bladed Curtiss Electric constant-speed propeller through a 16:11 gear reduction.
The GR1670A1 was also used in the Seversky SEV-S1, NR18Y, a record-setting experimental variant of the rival Seversky P-35.
Registration issued 1 June 1936, cancelled 26 April 1937.
The Curtiss-Wright Model 75 would be developed into the P-36 Hawk fighter for the U.S. Army Air Corps. France ordered it as the H75A-1, and in British service, it was known as the Mohawk Mk.I.
The tenth production P-36 was modified with a liquid-cooled Allison V-1710 V-12 engine to become the prototype XP-40.