The Delta M had a three stage configuration. The first stage was the Long Tank Thor, a stretched version of the Thor missile, previously flown on the Delta L. Three Castor-2solid rocket boosters were attached to the first stage to increase thrust at lift-off. A Delta E was used as the second stage, and the third stage was a Star-37D solid rocket motor. On the final flight, six boosters were flown instead of three, in a configuration known as the Delta M6, or "Super Six".
All thirteen launches were made from Launch Complex 17A at the Cape Canaveral Air Force Station. The first launch (carrying Intelsat 301) on September 18, 1968 was a complete failure when the first stage began suffering abnormal pitch gyrations shortly after liftoff. Around 1-1/2 minutes into launch, the vehicle became uncontrollable and began to disintegrate. Range Safety issued the destruct command at T+108 seconds. The fifth launch on July 25, 1969 (Intelsat 305) suffered a rupture of either the third stage casing or nozzle and ended up in an unusable orbit. Of the thirteen launches, twelve carried geosynchronouscommunications satellites. The thirteenth, which was the final flight and the only one in the M6 configuration, placed Explorer 43 into a highly elliptical orbit.