The protection which the V-51R Ear Plug provides against high-intensity impulse noise was determined for simulated rapid-fire field conditions. Twenty enlisted men were exposed to 2, 4, and 6 pounds per square inch peak overpressures generated by a 105mm howitzer. Their temporary threshold shifts were then measured at 2000 and 4000 cycles per second. The results indicated that inserting the V-51R Ear Plug without checking its fit does not give adequate protection to all personnel. It was also found that a protection-checked ear (ear plug inserted to minimize the level of a reference sound) gave adequate protection with impulse pressures up to 8 psi.iii CONTENTS ABSTRACT .