2P4 Mars2P2 Transporter-Erector-Launcher with 3R1 missile of 2K1 missile complex «Mars» in Saint Petersburg Artillery museum.
Janes states : The single-rail Filin (NATO designation Free Rocket Over Ground ,FROG-1) was carried on a modified IS-2 heavy tank chassis designated the 2P2. The shorter-range single-rail Mars (NATO designation FROG-2) was carried on the 2P4 non-amphibious variant of the PT-76 light amphibious tank chassis. Can anyone help us out?
Mars pictures:


Picture added on 27 August 2011 at 10:47
Maybe someone with more experience of Warsaw Pact AFV's could comment further.
Added by Stephen Prosser on 20 January 2014.