An embodiment of the rocket motor of this invention employs an insensitive munitions approach that, when subjected to elevated external temperatures, is activated by thermal expansion of the main propellant and gas generation from a secondary insensitive munitions charge. In a preferred embodiment, the rocket motor also includes a pressure equalizing system that accommodates changing temperature conditions during storage as well as varying gas pressure inherent in gun-launched systems in a manner that allows for thinner case cylinder design and increased propellant volume.