Shambolic gunners joke about first of tanks (6)
I believe the answer is:
ragtag
'shambolic' is the definition.
(ragtag can mean disorganised or chaotic)
'gunners joke about first of tanks' is the wordplay.
'gunners' becomes 'RA' (Royal Artillery).
'joke' becomes 'gag' (gagging is a kind of joking).
'about' indicates putting letters inside.
'first of tanks' becomes 't' (1st letter of 'tanks').
'gag' placed around 't' is 'gtag'.
'ra'+'gtag'='RAGTAG'
(Other definitions for ragtag that I've seen before include "Disreputable group of people" , "Mob" , "Disorderly" , "Masses" , "Disparaging term for the common people" .)