Hello!
This is a link to the Marksman AA tank in Finnish service so Im not sure if it is the same. It is mounted on a T-55 tank not a Chieftain tank here in Finland though. It is ingame in the Finnish OBAT by the name
Itpsv 91 AA if you want to look at it.
Heres the link:
http://www.mil.fi/maavoimat/kalustoe...y/00128_en.dsp