central tank, three interconnected, pressurized follower tanks feeding the central tank, and two additional follower tanks in the non-moving parts of the wing. The Su-17M was also fitted with the new SPO-10 Sirena-ZM radar warning receiver and the ARK-15 Tobol radio compass. The combat payload for the Su-17M was increased to four tons with the addition of two extra fuselage hardpoints, providing a total of eight BDZ-57M or MT hardpoints for carrying free-fall bombs. MBDZ-U6-68 hardpoints are also available for KMGU submunition containers, S-8 or S-25 rockets. The Su-17M could also carry the Kh-28 anti-radiation missile, which, used in concert with the Metel-A ELINT pod enables the aircraft to engage radar-guided air defence systems. Su-17M-28 Testbed for Kh-28 (AS-9 Kyle) anti-radiation missile Su-17MKG Testbed for Kh-25 and Kh-29 missiles Su-17R Small number of Su-17M aircraft equipped to carry reconnaissance pods. Equivalent export version designated Su-20R. Su-17M2 (S-32M2, "Fitter-D") Nose extended , with removed ranging radar and 'drooping' to improve pilot visibility. Equipped with the Fon-1400 laser rangefinder/marked-target seeker (LRMTS), ASP-17 and PBK-3-17s aiming avionics, RSBN-6S short-range navigation and instrument landing system. Features an undernose fairing for a DISS-7 Doppler navigation radar. The Su-17M2 first flew on 20 December 1973 with V. S. Ilyushin at the controls. It was manufactured between 1974 and 1977, and it entered service in 1975. The design of the Su-17M was further modified into what would become the Su-17M2, with three pre-production aircraft used as prototypes. The onboard avionics were improved - the KN-23 navigation system taken from the MiG-23 was installed, with an IKV inertial attitude indicator, a DISS-7 Doppler velocity sensor, air signal systems, and a V-144 analog computer with its own input panel. With the RSBN-6S Romb-K navigation system and the SAU-22M autopilot, the KN-23 provided the capability of automatically navigating along a route defined by three turning points before heading for the target location. The V-144 stored four sets of coordinates for landing airfields, and made it possible for the aircraft to automatically approach the airfield for landing and descend down to an altitude of 50-60 meters prior to manual landing. The SOD-57M transponder was replaced with the newer SO-69. During its service, the SRO-2M transponder was replaced with the newer Parol (Russian for "Password") system. A Fon-1400 laser rangefinder was installed under the inlet cone. The Delta NG missile control system, designed to send command signals to the Kh-23 Grom missile,