Answer:
Germany
Step-by-step explanation:
After World War II both the Americans and Russians use scientists and technology from GERMANY to help them improve their development of jets and Rockets.
This is because, during this period, Germany is known to have the leading knowledge and resources of making jets and rockets.
For example, the United States used the Operation paperclip to get many German experts including Wernher von Braun and his V-2 rocket team, to work for them in the United States on jets and rockets.
Similarly, the Soviet Union at this time also used Operation Osoaviakhim to get many German experts to build their Jets and Rocketry including Helmut Gröttrup, the former head of the group V-2 control systems in Germany.