The seeker was modified to work with a variety of guidance radars, including those being used with existing European missile systems. Production of the RIM-7H began in 1973 as NATO Sea Sparrow Missile System (NSSMS) Block I. For the US Navy's use the new Mark 95 illuminator system was also introduced, similar to the original Mark 115 but with automatic guidance that could be used in any weather. The Mark 95 formed the basis of the highly automated Mark 91 fire control system.