Delta 3914 was a three-stage Delta 3000-series configuration with an RS-27-powered extended long-tank first stage, nine Castor IV strap-on motors, the TR-201-powered second stage, and a TE-364-4 solid third stage. Twelve vehicles flew from 1975 through 1986. Ten reached their planned launch objectives; Delta 134 was lost after a strap-on motor failure, and Delta 178 was destroyed after a first-stage electrical failure.