While you make a good point the secret police forces of the 20th century would have killed for some of the surveillance tools they'd have access to of they trie

While you make a good point the secret police forces of the 20th century would have killed for some of the surveillance tools they'd have access to of they tried it over today. No need to steam open letters and read them physically, phone taps which can automatically surveil entire cities making connections between people, cameras able to follow people's vehicles without carefully coordinated follow teams. Who knows how the resistance would have faired under those conditions.