Watch a classified FM radio training video from WW2

That crisp signal was once a really big deal. The film was made for the military in 1944 and released to the public five years later. Breakthroughs, discoveries, and DIY tips sent six days a week. While fewer and fewer people are listening to FM radio today, it was hot stuff amid its widespread rollout during the late 1930s and early 40s. Short for frequency modulation, FM's appeal compared to AM (amplitude modulation) were immediately apparent: a clearer sound, less static, and more reliable transmissions.