An electronic cooling design and test approach utilizing a counter flow air-cooled heat exchanger is presented. The design is particularly applicable to military (i.e., Navy) weapon systems where extended reliability in harsh thermal and dynamic environments and simplicity of design are of paramount importance. Analytical modeling techniques were utilized to perform design tradeoffs, define heat exchanger air flow rates and predict steady-state semiconductor operating temperatures for worst-case duty cycles and ambient conditions. Environmental testing was conducted on an instrumented development unit to prove-out the cooling design and validate high reliability performance. This paper encompasses the cooling system selection and design and the environmental test results. Heat exchanger performance ratings as well as measured component temperatures are presented.