The player takes on the role of 'Super Joe', an elite Commando who is
equipped with a bionic arm; an ingenious device that acts as an advanced
grappling hook and must be used to traverse the many platforms and ledges
that make up the game's levels. The arm can also be used to destroy the
enemies that populate the levels, as well as to retrieve bonuses and
weapons that are occasionally dropped by parachute.
This game is known in Japan as "Top Secret".
Many Capcom employees consider this to be one of the most difficult games Capcom ever released in arcades. (arcade-history)