The SR-71 mainly had only one use. It was only used as a reconnaissance plane. It was filled completely with surveillance equipment except for a little space where two people could squeeze in. It was used for scoping out targets and spying on enemy bases. It was NOT stealthy, as most people might think at first glance. The equipment it was stuffed with were things like cameras and video cameras. After 1990, some SR-71s went to NASA for research. All of them were used in experiments such as a laser air-data collection system. The above mentioned are the uses for this magnificent plane.