The S-500 Prometey, also known as 55R6M “Triumfator-M,” is being designed to augment currently-deployed S-400 air defense systems. But according to other analyses and published reports, the S-500 is believed capable of challenging the most sophisticated U.S.-made stealth fighter aircraft — the F-22 and F-35 variants, and B-2 bombers. The National Interest reported in April 2017 that the S-500 would likely include “the 91N6A(M) battle management radar, a modified 96L6-TsP acquisition radar, as well as the new 76T6 multimode engagement and 77T6 ABM engagement radars.”