What you are talking about is called Convergent Evolution. Basically where different players (or species) arrive at the same solution (or design) since it is the best for that particular task. This is why all the next-gen UCAVs will look more or less the same, why modern Western tanks all look quite similar, and why formula One vehicles look like clones of each other to the untrained eye.
In animals it is quite widespread, and there are a plethora of such examples.
And my personal all time favorite ....the American Bald Eagle versus the Kenyan Fish Eagle.
Bald Eagle:
Kenyan Fish Eagle:
With that said, it is common knowledge that a bunch of Soviet stuff was stolen US tech. A prime example is the Buran space shuttle, which was derived from the NASA shuttle (the Soviets feared that the Shuttle was some sort of space weapon delivery system, and thus they needed to have one too). But all the same convergent evolution does exist in tech and weapons (the tricky part is deciding what is convergent evolution and what is due to sticky fingers).