Earth vs. the Flying Saucers (1956)

While driving through the desert to a military base where an eleventh rocket will be sent into Earth's orbit to assist the exploration of outer space in Operation Sky Hook, Dr. Russell A. Marvin and his wife, Carol, see a flying saucer and accidentally record a message on their tape recorder. Once at the base, Dr. Russell is informed by his father-in-law and general that the first ten rockets mysteriously fell back to Earth. When Dr. Russell decodes the message, he encounters the aliens, who ask him to schedule a meeting with the leaders of Earth in Washington, DC, in 56 days in order to invade Earth without panicking the population. Dr. Russell develops an anti-magnetic weapon that becomes the last hope of the human race against the hostile aliens.