Quoted from Wikipedia: "The Sukhoi Su-15 (NATO reporting name: Flagon) was a twinjet supersonic interceptor aircraft developed by the Soviet Union. It entered service in 1965 and remained one of the front-line designs into the 1990s". The early Su-15 ("Flagon-A") had pure delta wings like its predecessors, but these were replaced from the 11th production series onward by a new double-delta wing of increased span and area, with a small wing fence above each outer pylon and blown flaps to improve landing characteristics. This was accompanied by a new tail of greater anhedral and a vertical fin of reduced height.
Quoted from Airvectors.net: In the mid-1960s, one Yak-28L was converted to a "defense suppression" -- or, as the Americans would say, "Wild Weasel" -- configuration, fitted for carriage of two Kh-28 (NATO AS-9 Kyle) anti-radar missiles in place of the wing tanks, with the bombing system replaced by a radar homing and warning system (RHAWS) to target radars.
This machine was designated "Yak-28N", where "N" stood for "Nositel (Carrier)", meaning "missile carrier". The conclusion of the exercise was that a more modern machine was needed for the tough defense suppression mission, and the Mikoyan MiG-25BM "Foxbat-F" was obtained for that role instead.
In roughly the same timeframe, another Yak-28I was modified as a radar reconnaissance machine, carrying a "Bulat (Damask Steel)" side-looking airborne radar (SLAR) in the bombbay, with the SLAR antenna deployed out
of the bombbay when observations were to be made. This machine was redesignated "Yak-28BI". It also was not adopted for service.
However, an electronic countermeasures variant, the "Yak-28PP", where "PP" stood for "Postanovschshik Pomekh (Countermeasures Aircraft)", did go into service. The Yak-28PP was developed in the late 1960s
and entered production in 1970. It was something of a hybrid, with the cockpit and canopy of the Yak-28R, but the nose glazing of the Yak-28L; exactly why a countermeasures aircraft needed nose glazing is an interesting little question.
The Yak-28PP was crammed full of countermeasures gear, leading to a clutter of antenna fairings over the fuselage. The Yak-28PP was unarmed, but it could carry a pod of 57-millimeter rockets on each outer wing, with the rockets carrying warheads full of chaff to blind adversary radars; the aircraft was also fitted with chaff-flare dispensers for self-defense. The Yak-28PP was designed to accompany attack aircraft as they penetrated hostile airspace, using its jammers and chaff rockets to protect the strike package. Total production of the Yak-28PP is unclear.
This variant of the Su-15 dubbed Su-15MP (NATO reporting name: "Mantra") was only briefly operated in Afghanistan probably for trials and testing. It's role was like the Yak-28PP (to which it probably should have been a successor) of as a Wild Weasel.
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It incorporates a reworked and highly modified Su-15 fuselage. Wings and tail sections seems to be entirely new and seem to incorporate some
early stealth technologies like a blended intake, angled fuselage and canted tail to hide the exhausts. The exhausts are possible of an early vectoring thrust type although this is highly speculative. There seems to be no means of self defence so probably relies on the element of surprise, chaff/flares and it's agility, although the lumps and bumps indicate a wide range of ECM equipment and most likely an elaborate jamming suit.
Little is known about the Su-15MP as it seems to be an one off highly secretly experiment in early stealth technology. It was never seen again after 1988.