Essential equipment for invaders from Mars (4)
I believe the answer is:
arms
'essential equipment' is the definition.
'arms' can be an answer for 'equipment' (I have seen 'military equipment' mean 'arms' so perhaps 'equipment' could also mean 'arms'). I am not sure about the 'essential' bit.
'invaders from mars' is the wordplay.
'mars' anagrams to 'ARMS'.
But, I am not clear how this is indicated.
'for' acts as a link.
Can you help me to learn more?
(Other definitions for arms that I've seen before include "Guns et cetera" , "pacifists won't take up" , "Protesting violently, up in these" , "Weapons and limbs" , "Crest - guns" .)