This paper discusses the design and performance results of a modular designed spark ignited rotary engine Auxiliary Power Unit (APU) fueled by JP-8. This APU is intended for use onboard tactical and combat vehicles applications where packaging space and weight are at a premium. The platform is flexible and scalable to allow for application to the full portfolio of tactical and combat systems. Such an APU would enable the Army to realize significant cost savings in terms of fuel and fuel support, as well as enable enhanced operation modes of existing vehicles by enabling Silent Watch capability.