There are many demands for interoperability between weapon systems as the operational needs for joint and coalition based on network in modern and future warfare have been increasingly needed. In DoD, LISI has been applied throughout information system life cycle from the planning phase to the development phase to assess the level of interoperability. We also developed SITES which is a tool to assess the level of interoperability in information systems. But we should extend the assessment model from the previous information systems to the weapon systems to assess the level of interoperability including weapon systems as well as information systems. In this paper, we proposed the assessment model of interoperability, implemented the E-SITE based on the proposed model, applied 12 weapon systems and analyzed the experimental result.