Propulsion systems for military applications, especially for ground combat vehicles, operate in harsh environments and must fulfill a long list of challenging technical requirements. High power density, fuel efficiency, multi-fuel capability, reliability and serviceability are only a few of the top level requirements that cascade down to many sub-system requirements. As part of the Combat Vehicle Prototyping (CVP) program, the US Military is focusing on opposed piston engine technology to meet the requirements for the Advanced Combat Engine (ACE). Globally, opposed piston engines have no considerable presence in commercial applications and have been mostly replaced for military applications. This paper reviews the opportunities and challenges with opposed piston engine technology and introduces an advanced high-performance 4-stroke engine solution as alternative for the ACE.