Name my regiment (4)
I believe the answer is:
myra
'name' is the definition.
'my regiment' is the wordplay.
'regiment' becomes 'RA' (Royal Artillery).
'my'+'ra'='MYRA'
(Other definitions for myra that I've seen before include "Girl's name" , "Dame --- Hess; Vidal's Breckinridge" , "Woman's name, anagram of army" , "Girl" , "- - Breckenridge (novel)" .)