Operation Crossbow (1965) on Netflix

In an effort to learn more about German rocketry, the Allies infiltrate the Nazi missile works at Peenemunde. The agents they have selected are all engineers and they assume the identities of real-life individuals who are either dead or otherwise indisposed. What they don't realize is that the mission has been compromised from the beginning by the fact that one of them men is wanted for murder and that one of the applicants for the mission is actually a Nazi agent. In the end, the two remaining agents assist the RAF in identifying the works site during a massive bombing campaign.