A little-known and poorly-documented proposed variant of the Titan family of launch vehicles, the Titan IIIG used an increased-diameter core with 156-inch diameter solid rocket boosters. The late-1960′s Titan IIIG would have been capable of launching 100,000 pounds, and seems to have been focused on USAF missions. McDonnell Douglas appears to have considered it for use in launching the Big Gemini logistics capsule. Beyond that, not much is known. The McD illustration below is one of the few I’ve come across, and does not seem likely to be terribly accurate. Also depicted here are the Titan IIIM, a launch vehicle composed of a cluster of four 156-inch solids topped by an S-IVb stage (a McD product), a 260-inch solid topped by an S-IVb, and external tank arrangements for reusable launch vehicles such as the ILRV (integral Launch and Recovery Vehicle), a predecessor to the Space Shuttle. McD’s entry to the ILRV study was a derivative of their generic Model 176 concept.