Berliner-Joyce P-16

After the Berliner Aircraft Company was adquired by the newly established Berliner-Joyce Aircraft Corporation in February 1929 with the aim of developing a monoplane but, they got involved in the development of a two-seater biplane for the United States Army Air Corps.
The prototype, named XP-16, flew for the first time in October 1929. It featured an all-metal structure with a fabric covering. It was a single-bay biplane of unequal span and the wings forward-staggered. Lower wing was smaller that the upper one that was mounted on the base of the fuselage in a sesquiplane fashion and, unusually, of the reverse-gullwing type. An observer/gunner post was located just behind the pilot armed with 0.30in Browning machine gun mounted on an scarff ring. It was powered by a 600hp (447Kw) Curtiss V-1570 Conqueror supercharged V-12 inline engine.
It was evaluated by the USAAC and two contracts were awarded for a total of 25 pre-production aircrafts named YP-16 with the main difference being that it was powered by a non supercharged version of the Conqueror engine and that it drove a two-bladed propeller instead of a three-bladed one.
During 1931 the USAAC ordered the YP-16, the pre-production version, which was the last biplane to enter service with the USAAC. Furthermore, the P-16 was the only two-seat biplane fighter to be produced for the army after 1918. It was delivered in 1932 to the 94th Pursuit Squadron and, as most of them were of the YP-16 type and weren't powered by the supercharged version of the engine, performance at altittude was greatly reduced, although it had better endurance than contemporary single-seat fighters. Visibility was poor in spite of the gull-wing and due to that it was prone to nose-overs when landing.
All of them were withdrawn from active service in 1934, although some of them remained in second line duties until 1940.

Sources:
1. https://en.wikipedia.org/wiki/Berliner-Joyce_P-16
2. Salamander Books - The Complete Book of Fighters