This paper addresses evolutionary improvements that have been made to aircraft environmental control system (ECS) equipment, using the C-130 ECS as an example. The paper traces the history of the C-130 aircraft and its variations and describes changes made to the ECS equipment to keep up with increased cooling demand. In particular, the paper discusses improvements to the C-130 simple-cycle refrigeration unit and, to a lesser extent, to the ECS as a whole. These improvements integrate technology advances from government-, prime contractor-, and AiResearch-funded programs on various military aircraft. These advances have been applied to requirements for upgrading both the basic C-130H airplane and the Special Operations configuration. The ECS improvements involve cooling performance, structural integrity, and reliability/maintainability enhancements.