The Delta 1000 series introduced an extended long-tank Thor-derived first stage with the Rocketdyne MB-3 engine and a universal boattail. Flown configurations used four, six, or nine Castor II strap-on motors, either the 1.65-metre or 2.44-metre AJ10-118F-powered second-stage arrangement, and optional TE-364 solid third stages. Eight vehicles flew successfully from September 1972 through June 1975 across six exact configurations.