Turkey, a NATO ally, recently arranged to purchase four Russian-made S-400 mobile missile batteries at a cost of $2.5 billion over the next several years. However, according to Pentagon officials, the Russian surface-to-air-missile systems are not compatible with NATO air defense systems. The deal was first reported last February in Sputnik News.
Defense Secretary Jim Mattis commented in a press room gathering, “The problem is, is how do you interoperate with NATO systems with Russians — they’ll never interoperate,”
The S-400 Triumf (Russian: C-400 Триумф, Triumph; NATO reporting name: SA-21 Growler), previously known as the S-300PMU-3, is an anti-aircraft weapon system developed in the 1990s by Russia's Almaz Central Design Bureau as an upgrade of the S-300 family. It has been in service with the Russian Armed Forces since 2007.
The mobile long-range surface-to-air missile system has been designed to intercept electronic warfare airplanes, as well as early-warning and surveillance aircraft amid aggressive electronic jamming.
The S-400 uses four missiles to fill its performance envelope: the very-long-range 40N6 (400 km), the long-range 48N6 (250 km), the medium-range 9M96E2 (120 km) and the short-range 9M96E (40 km). The S-400 has been described, as of 2017, as "one of the best air-defense systems currently made."