U-2s have taken part in post-Cold War conflicts in Afghanistan and Iraq, and supported several multinational NATO operations. Beyond tactical surveillance, U-2s have supported the development of electronic sensors, calibrated space-based instruments, conducted high-altitude atmospheric experiments, and tested line-of-sight and over-horizon communications systems. The U-2 is one of a handful of aircraft types to have served the USAF for over 50 years, along with the Boeing B-52, Boeing KC-135, Lockheed C-130 and Lockheed C-5. The newest models (TR-1, U-2R, U-2S) entered service in the 1980s, and the latest model, the U-2S, had a technical upgrade in 2012. The U-2 is currently operated by the USAF and NASA