Aware that he was about to be drafted to fight in the Korean War Sullivan wanted to become an Army diver, so he left the University of Washington to attend the Sparling School of Deep Sea Diving in Long Beach, California.
[1] Due to his civilian training he went overseas to Korea in 1954, where he was assigned by the Army to be a diver to repair oil pipelines and other facilities damaged during the US invasion of Inchon Harbor.
[1][2] Sullivan is largely responsible for the Ultimax 100 light machine gun and the SureFire MGX.
[4] In 2014, Sullivan provided a video interview regarding his contributions to the M16/M4 family of rifles while working for Armalite.
In the video, he demonstrates his "Arm West LLC modified M4", with enhancements he believes necessary to rectify the issues with the weapon.