First thing to bear in mind is that there are actually TWO movies ,made at the same time,dealing with the same subject :a true life event of ex-firebrands using the sewers to rob a bank.
-The French version,made by Jose Giovanni , ("les egouts du paradis" = sewers of paradise (sic))which kept the hero's real name but is rather listless. The "hero" becomes a nice guy ,some kind of Arsene Lupin,who visits the old ladies in the hospital.
-The English version,which features a best lead (Ian McShane billed as "Brain") and seems more honest.Far from being heroes,like in Giovanni's flick,the characters are fascists (anti communist) and their paramilitary activities are not passed over in silence :in the French attempt,all they show is weapons in the thieves' den in the country.