Interoperability between heterogeneous software systems is an important issue to increase software reusability in the software industry. Many methods are proposed to implement interoperable systems using distributed computing infrastructures such as CORBA, HLA and SOA. Those infrastructures can provide communication channels between software systems with heterogeneous environments. SOA (Service Oriented Architecture) provides a more flexible approach to interoperability than do the others because it provides platform independence and employs platform-neutral message passing with Simple Object Access Protocol (SOAP) to communicate between a service and a client.The main contribution of this study is to design and implement an interoperable DEVS simulation environment using the SOA concept and a new construct called the DEVS namespace. The interoperable DEVS environment consists of a DEVS simulator service and an associated integrator. The DEVS simulator service provides both simulator level and model level interoperability. Moreover, using the DEVS namespace, DEVS simulator services can be interoperable with any services using the same message types.To demonstrate the utility of the proposed environment, we describe various applications of the interoperable DEVS simulation environment. The applications are drawn from real world development of automated testing environments for military information system interoperability. A radar track generation and display federation and a model negotiation web service illustrated the ability of the proposed middleware to work across platforms and languages. Its ability to support higher level semantic interoperability will be demonstrated in a testing service that can deploy model agents to provide coordinated observation of web requests of participants in simulated distributed scenarios.