Soviet spies were astonishingly effective in the 1940s. They were sending back literal plane loads of documents during lend-lease. What helped the soviets th

Soviet spies were astonishingly effective in the 1940s. They were sending back literal plane loads of documents during lend-lease. What helped the soviets the most were not bomb secrets, but factory plans like rubber tire plants, oil refineries, metal stamping plants. We gave them a lot of this stuff for free in lend/lease but they still used spies to make sure we were not feeding them disinfo. For the atomic program, Beria used the intelligence reports mainly as a way to make sure his own scientists were not wasting time/resources/money. The soviets were terrified of insider attacks slowing progress, so intel provided a yardstick to measure against.