A drop hammer for driving a pile. The drop hammer of the present invention comprises a housing member, a ram member, a helmet member, and a lifting system. The housing member defines a housing chamber and a vent port defining a preload position. The ram member is supported for movement within the housing chamber. When the lifting system raises the ram member above the preload position, ambient air substantially freely flows into and out of the housing chamber through the vent port. When the ram member falls below the preload position, ambient air within a preload chamber portion of the housing chamber compresses to apply a preload force on the inner portion of the helmet member. When the ram member moves into the lower position, the ram member impacts the helmet member to force the helmet member from the rest position to the impact position, thereby driving the pile.