No secret can't be uncovered using a single truth-telling serum. If there was, then two truth-telling serums would suffice.
The F soldiers were also certainly not soft, especially Kluse who has lost one of his hand. He kept his mouth shut about this throughout, but with the truth-telling serum, mental fortitude was useless.
Celebrate the glory of technology.
41 F soldiers were captured, and 59 soldiers died in the crossfire. Ivan treated the execution of this mission carefully. Not only did he leave radio communication records, but he also recorded the entire duration of the second warning. Then the subsequent resist to cooperate, and the firing of anti-air machine guns was recorded by the cameras on the helicopters.