here is a later version of the same name (with the guncar @Svenn made)
an interesting HP You probably already know
http://derela.republika.pl/armlok2.htmand here an Austrian picture
which makes me think - The engine appears to be a tank Loco...
Which would make a tender unnecessary
However the fact that the polish included additional space for wood implies that the range might have been a bit limited....
later armoured trains always have tender engines
anyway, this seems to be "Smialy" with a tank Loco
and maybe here the car behind the assault car could be a tender?
Anyway, whether You want to add a tender or not, tenders are rather universal and basically a big square water tank with a small box for coal/wood on top, especially when armoured