This is not a shirt, It is a smock.
Im afraid youll find it isnt
They label it as a jacket but it is in fact a shirt,certainly not a smock.
Definitely a jacket – hence the zip - but very thin cloth because it was designed for wear in hot climates i.e. tropics.
NB Soldier 95 (and later) issues had a similar design of item which was labelled as “jacket, lightweight”
Often worn as a shirt in UK/Germany in the 1970’s & early 1980’s in preference to the issue KF Shirt because
(a) it was camouflaged not green so the smock could be taken off on hot days
(b) it was not made of wool and so did not itch like crazy
(c) it made you look like you had done the Jungle Warfare Course
Often banned by RSM's because the colour was "redder" than normal DPM or because (allegedly) the high nylon content, which was to stop it rotting in hot & humid enviroments meant it would melt on to you if there was a "flash fire" nearby.
Rumour has it that it was because so many people were wearing these jackets that the very similar S95 design of lightweight jacket was created.