Spent 3 years in the early 80s servicing the SR-71 in the air on the KC-135Q model tankers all over the planet. We would be going placard airspeed during aerial refueling and they were going as slow as they could to maintain flight. When they would start to get heavy the pilot would always let you know he was lighting an afterburner (especially at night) so he could maintain flight. Really cool to see that purple cone of fire shooting out the back of the engine. Since the aircraft didn’t have fuel bladders you could tell he was getting full when fuel was running down the back of the aircraft. Once refueling was complete the tankers would make an immediate left-hand turn to get out of the SR-71s way as they were cleared to 60,000 ft to go on their supersonic portion of the mission.