I'm currently reading "Dark Sun: The Making of the Hydrogen Bomb". The first section of the book focuses on the Russian A-Bomb program in the 1940s and how much of it was accelerated through espionage conducted against the US and UK. I'm struck by how painful a slog spying was. These spies were always effectively working two jobs and much of the nuts and bolts of spying and conveying information to handlers sounds like boring, thankless work. Often, the spies were not paid at all. There are excerpts where handlers bemoan the difficulty and lack of compensation of their spies. All-in-all, it sounds like a crappy job. You really had to be a true believer, I guess.
And yet, in the 1940s at least, the Soviets were absolutely looting the Americans. During the lend-lease program between the US and Russia, planes were flown out of Montana to the USSR. US military officers recalled Soviets flying dozens of large briefcases on each flight. Once, a US officer inspected those briefcases and found detailed factory schematics, product and process diagrams and plans, reels and reels of detailed photographs of machinery and parts, and classified documents on the R&D of uranium enrichment. Apparently, in light of this discovery of massive industrial theft, the U.S. took no action.