On May 17th, 1974 the first Synchronous Meteorological Satellite or SMS-1 was launched on a Delta 2000 series rocket. The SMS-1 and SMS-2 satellites were the first purpose-built geostationary weather satellites ever launched and these missions started a long lineage that leads to the present day GOES missions.

http://www.space.com/34779-goes-r-weather-satellite-launched-atop-atlas-v-rocket-video.html