Abstract: An apparatus adapted for drilling earth formations, earth structures or the like essentially embodies an outer tubular means, hollow drill bit means, hammer assembly mechanism, and a rupturable interconnection means. The outer means is rotatable and axially movable having a drilling end insertable within the earth. Connected adjacent the drilling end is the hollow drill bit means which is conjointly rotatable with the outer means. Such outer drill bit means has an anvil impact shoulder formed on the interior surface thereof. The inner drill bit means is located within the outer member and is arranged, in a preferred embodiment, to be conjointly rotatable therewith. A percussion shoulder is integrally formed on the inner drill bit means and is arranged to selectively impact the anvil impact shoulder.