Not always true, some of the America major technological advancements comes with those ex-Nazi Scientist who were given a choice to either face the rope or work for them , V2 rocket is one of the many example which was the baseline for all Ballistic missiles of future .
Actually in this example you mean major German technical advances came from the help of an American.
https://www.nasa.gov/feature/goddar...oddard-s-rocket-and-the-launch-of-spaceflight
NASA Celebrating 90 Years: Robert Goddard’s Rocket and the Launch of Spaceflight
Less than a century ago, astronomers relied entirely on ground-based observations to further scientific study. Today, descendants of that first liquid-fueled rocket provide eyes on cosmic phenomena, unravel mysteries of the early universe, and even take a closer look at what makes our own planet tick.
None of this would be possible without the experiments of Massachusetts physics professor Robert Goddard,
best known for inventing the liquid-fueled rocket. The namesake of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, he dreamed as early as 1909 of creating an interplanetary vehicle. While he couldn’t achieve that in his lifetime, his inventions in the first half of the 20th century became the engineering foundation for the rockets that first took humans to the moon in the 1960s and for today’s rockets, which look further into space than ever before.
Prior to Goddard’s experimentation, rockets had not changed much in several centuries. Chinese engineers invented them as war machines in the 13th century, using solid gunpowder as fuel. But Goddard realized that liquid propellants offered a number of advantages over solid-fueled rockets. He began to test rockets fueled by liquid gasoline and liquid oxygen.
The new design posed a number of challenges. For instance, he had to find a way to mix the fuel with oxygen. Otherwise it wouldn’t burn fast enough to produce the necessary thrust to lift the weight of the rocket. He also had to find a mechanical solution to pressurize the fuel chamber so it would continually feed fuel to the engine. Each solution he found brought with it a new challenge to solve.
After nearly 17 years of work,
Goddard successfully launched his creation on March 16, 1926.
https://en.wikipedia.org/wiki/Wernher_von_Braun
"...Before 1939, German scientists occasionally
contacted Goddard directly with technical questions. ...
Goddard confirmed his work was used by von Braun in 1944, shortly before the Nazis began firing V-2s at England."