We consider the problem of sensor-mission assignment as that of allocating a collection of intelligence, surveillance and reconnaisance (ISR) assets (including sensors and sensor platforms) to a set of mission tasks in an attempt to satisfy the ISR requirements of those tasks. This problem is exacerbated in a coalition context because the full range of possible ISR solutions is not easy to obtain at-a-glance. Moreover, the operational environment is highly dynamic, with frequent changes in ISR requirements and availability of assets. In this paper we describe a solution for the sensor-mission assignment problem that aims to maximize agility in sensor-mission assignment, while preserving robustness. The search space of potential solutions is reduced by employing a semantic reasoner to work out the types of sensor and platform bundles suitable for a given set of ISR tasks. Then, an efficient resource allocation algorithm is used to assign bundles of sensor/platform instances to satisfy each task, within the search space determined by the reasoner. The availability of instances takes into account access rights on those instances across the coalition's inventory. We describe a proof-of-concept implementation of this approach, in the form of a decision support tool for ISR planning. We illustrate the approach in the context of a coalition peace support operation scenario.