In 1970 the U.S. Army fielded the Sound Protective Helmet No. 4 (SPH-4) as its new aircrew helmet and, with improvements, it has been used continuously since that time. The SPH-4, a single visor, lighter weight version of the Navy SPH-3, replaced the two Army aircrew helmets then in use: The Navy-developed Aircrew Protective Helmet-No. 5 (APH-5) and the Army-developed Antifragmentation Flight Helmet-No. 1 (AFH-I). Both helmets were deficient in noise attenuation and retention capability. The SPH-4, which was specifically designed for sound protection, pro- vided (and still provides) superior sound attenuation, but the 1970 version provided no more impact protection than the APH-5..