Over the past 4 years, military groups have had under development components and accessory parts for electronic equipment destined for ultra-high-temperature and intense nuclear radiation applications. High-speed flight, an approach to miniaturization and reentry problems all promise ambient temperatures for electronic gear as high as 500 C (degrees centigrade). The anticipated launching of a nuclear-powered aircraft introduced the new environmental requirement, nuclear radiation. One of the component developments concerned is for 500 C electronic power transformers and has been sponsored by the Air Force under two contracts, AF33(616)-3623 and AF33(616)-5579. The purpose of this and a companion paper, Part II,1 is to summarize the outcome of this development in a form meaningful to design engineers. Design considerations, the subject of this paper, examines the basis for the selection of materials, their mechanical arrangement, and the calculation of coil temperature rise. Using these essential data, Part II1 then presents a digital computer optimization procedure that yields a minimum-weight transformer design.