It was a top secret, and yet the enemy knew. They knew that the Americans were about to send a manned rocket to the moon and thereby claim it for Old Glory. They knew also that whoever held the moon would command the Earth ... and they were determined to stop us at all costs!
When assassination and sabotage failed to stop the take-off, they'd have to use even more drastic measures. There might be an H-bomb loaded rocket missile, there could be a Red spaceship with a suicide crew, and there was always the possibility of their placing a spy aboard the U.S. rocket.