Delta 3913 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 solid third stage. Its sole flight launched Dynamics Explorer 1 and 2 in August 1981. A second-stage propellant-loading error reduced performance, but both spacecraft reached usable coplanar polar orbits and completed productive missions.