Marshal reserve force at home after exercises (6)

'marshal reserve' is the definition.
'Petain' can be an answer for 'marshal' (Philippe Ptain, WW2 French marshal). I'm not sure about the 'reserve' bit.

'force at home after exercises' is the wordplay.
'force' indicates an anagram (letters must be forced into a new order).
'home' becomes 'in' ('he's home' can mean 'he's in').
'after' says to put letters next to each other.
'exercises' becomes 'pe' (Physical Education class).
'at' with letters rearranged gives 'ta'.
'ta'+'in'='tain'
'tain' put after 'pe' is 'PETAIN'.

Can you help me to learn more?