Tactical networks are constrained networks that may transition between ad-hoc and mesh configurations and are characterised by frequent disruptions, changes in connectivity, and available resources. Whilst deploying a service-oriented architecture (SOA) allows the efficient provisioning of services at the tactical level, the existing resource limitations and potential attacks, require the dynamic adaptation of both quality of service (QoS) and security mechanisms. Within this environment, security and QoS must not only enforce the requisite functionalities, but also cooperatively seek optimal solutions for them according to their corresponding constraints and requirements. In this paper we propose a multi-domain policy-based decision subsystem supporting service delivery, that relies on an online knowledge-based reasoning mechanism. We describe the characteristics of such subsystem and show its benefits in relation to specific tactical requirements.