Be short of fuel? Submarine out of south has tons (8)
I believe the answer is:
undereat
'be short of fuel?' is the definition.
(fuel can mean food)
'submarine out of south has tons' is the wordplay.
'submarine' becomes 'undersea' (submarine means under the sea).
'out of' is a deletion indicator.
'south' becomes 'S' (synonyms).
'has tons' becomes 't' (I am not sure about this - if you are sure you should believe this answer much more).
'undersea' with 's' removed is 'underea'.
'underea'+'t'='UNDEREAT'
(Another definition for undereat that I've seen is " Take too little food".)