Not the US or the Soviet Union but Japan was the country that owned the first jet fighter in the Pacific Theater during World War II, with the first prototype being the Nakajima Kikka.
Nakajima Kikka appeared at a time when the war was almost over and the fate of this jet fighter model ended with the demise of the Japanese Empire.
The Japanese started the idea of developing a jet fighter when Japanese military officials witnessed test flights of the Messerschmitt Me 262 developed by Nazi Germany in 1944. Immediately, the Japanese Navy at that time realized the great potential of a jet fighter model in air combat. After a long period of preparation, Japanese aircraft manufacturer Nakajima was chosen to develop the first jet fighter for the country’s navy. And of course the new fighter had all the characteristics of a carrier-based fighter that would serve on Japan’s future aircraft carriers at that time.

Nakajima’s engineers at that time had to ensure some of the requirements of the Japanese Navy for the new fighter. The fighter had to be easy to produce and not require highly skilled workers, and its wings could be folded to suit aircraft carrier operations. And finally Nakajima released the first Nakajima Kikka prototype, also known as the Nakajima J9Y. It had a design quite similar to the German Me 262 aircraft model and was also equipped with two jet engines.
The first Nakajima Kikka prototype was tested on the ground at the Nakajima factory on June 30, 1945 and in July it was transferred to Kisarazu naval base to prepare for its first test flight. On August 7, 1945, Nakajima Kikka was officially tested and piloted by Major Susumu Takaoka of the Japanese Navy.

Compared to the Me 262, the Kikka’s fuselage was smaller and had many design features of Japanese fighters developed at that time with straight tail and main wings. Even the Kikka main landing gear was used from the legendary Japanese A6M Zero light fighter and the Yokosuka P1Y bomber. Despite significant progress, the subsequent Nakajima Kikka development program did not go very well, although at that time two prototypes were almost complete, along with between 18 and 25 pre-produced airframes.
However, all the Japanese Navy’s efforts to develop Nakajima Kikka were almost in vain when the country surrendered to the Allies on September 2, 1945, and this led to the end of the Nakajima Kikka program. And when the US disarmed the Japanese, Nakajima Kikka became a better trophy for the US Army’s jet fighter development program. Two prototypes were brought back to the US but they were both incomplete. However, thanks to acquiring almost the entire Nakajima factory, finding replacement parts for the Kikka was still quite easy.

It is quite interesting that before the end of World War II, Japan had developed many variants of the Nakajima Kikka including a two-seat training variant, a fighter reconnaissance variant, and a fighter variant with a main weapon system consisting of two 30mm Type 5 automatic cannons and 50 rounds of ammunition.
Nakajima Kikka’s jet engine system was also developed based on the German BMW 003 jet engine model with the Ishikawajima Ne-20 prototype with 4.66 kN each. Nakajima Kikka had a maximum flight speed of about 696km/h with a range of 1,778km. Nakajima Kikka’s maximum takeoff weight was 3.9 tons with a main wingspan of 10 meters and a weight of about 2.3 tons. After being shipped back to the US and completed, a Nakajima Kikka was able to fly continuously for 11 hours and 46 minutes in a test flight.