Original sentence: The National Weather Service added them to the existing network of the WSR-57 model to improve forecasts and severe weather warnings.WSR-74 RADARs are Weather Surveillance Radars designed in 1974
Edited sentence: Some have been sold to other countries.They were added them to the existing network of the WSR-57 model to improve forecasts and severe weather warnings.WSR-74 RADARs were Weather Surveillance Radars designed in 1974 for the National Weather Service