As the capability and utility of simulation across Defense grows, it is becoming increasingly important to understand if each simulation system is fit for purpose, well understood and meets distributed simulation interoperability requirements. To support this, the UK Ministry of Defence's (MoD) Defence Training and Education Coherence (DTEC) approach has developed a set of compliance rules and identified a number of international standards that must be employed, or at the very least demonstrate (from the Enterprise level Value for Money perspective) why they have been discarded. These rules compel system developers to investigate and employ the standards, best practices and resources in which UK MoD has invested. To further support these developments UK MoD is beginning to develop Defense-wide capabilities, delivered as services, to provide common simulation components and resources. Distributed simulation offers increased opportunity to train collaboratively across national boundaries. With the High Level Architecture (HLA) the preferred NATO interoperability standard, initiatives (such as MSG-134 Distributed Simulation Architecture & Design, Compliance Testing and Certification) are investigating and developing tools for HLA certification. The MSG-134 output will support interoperability testing enabling national and international activities. There is also potential for the development of a UK Distributed Simulation Management Service for Defense that could, for example, manage interoperability software (e.g. the HLA Run Time Interfaces (RTIs)), network performance, interoperability exchange definitions (e.g. the NATO Education Training Network (NETN) Federation Object Model (FOM) modules) and the certification of HLA federations. This paper describes a potential option that the UK MoD is investigating to develop a coherent testing capability that will support the evaluation of simulation components and the certification of simulation systems interoperability at a national and international participant level. The paper highlights key programs where certification would be required, outlines what a certification service might look like and identifies initiatives that will support the development of such a service.