pile cap 20 which transmits the impact energy of the ram upon the anvil down to a pile not shown or other element to be driven the anvil 18 is provided with a central cavity 22 which is open at the upper surface of the anvil and in this cavity there is provided a gas discharge device 24 the details of the gas discharge device form no part of the present invention and therefore they will not be described herein suitable such devices are described in detail in u s pat no 3 310 128 no 3 379 273 no 3 817 335 no 3 892 279 and no 3 958 647 the gas discharge device 24 accumulates a charge of gas such as air nitrogen etc at a very high pressure and then upon receipt of a triggering signal the pressurized gas charge is suddenly released into the surrounding region triggering may be effected by means of electrical signals generated at a remote location e g from a vessel or other structure situated above the surface of the water in which the hammer is submerged in operation of the hammer as thus far described the hammer is situated under water with the ram 10 resting on the upper surface of the anvil 18 when the gas discharge device 24 is triggered the sudden release of gas drives the ram 10 up inside the guide tube 12 the ram continues upwardly within.