Soviets also benefited a lot from German scientists pulled from post-WW2 Germany in their own version of a Paperclip-like program. Recommended reading: Forgotten Creators by Todd Rider. Free and online, over 4,000 pages including references and important appendices, so one has to navigate to the chapter / section of interest.

https://riderinstitute.org/revolutionary-innovation/

This is the same Todd Rider whose PhD work at MIT (advised by the late Lawrence Lidsky) showed aneutronic fusion was unlikely to be workable. Lidsky had previously argued DT fusion wasn't going to cut it because of inherently low volumetric power density and had argued aneutronic fusion should be pursued. Between those two approaches lies lower neutronicity D-3He fusion, which may be fusion's only real hope. Helion has the lead in pursuing this approach, with a design focusing on highly efficient energy recirculation that feels informed by Rider's analysis.