While more can always be said -- especially since this is an older thread -- you may enjoy reading

I know the Soviets have reverse engineered some western weapons/warplanes. What instances are there where the US reverse-engineered Soviet or Chinese military hardware?

with contributions by /u/tinian_circus, /u/pronhaul2012, and /u/kieslowskifan. A relevant quote:

The Alfas' titanium hulls illustrate one of the rationales why the US did not devote much effort to reverse-engineering Soviet technology: most US analysts took a default position that the Soviets were behind the West. This is why when the Soviets surprised the West, often analysts went in the other direction and engaged in a near hyperbolic overestimation of Soviet capabilities. When naval intelligence indicated that the Soviets were creating full-hulled titanium hulls in 1969-70, some CIA and naval intelligence hands felt that the Soviets could not master the technology to make full titanium welds, even when presented direct evidence such as titanium scraps that the US naval attache "acquired" in Leningrad. Although the West had used titanium in aerospace, most famously in the SR-71, the ability to make these welds on such a large scale was unprecedented.