With the achievement of autonomous flight for small unmanned aircraft, currently ongoing research is expanding the capabilities of systems utilizing such vehicles for various tasks. This allows shifting the research focus from the individual systems to task execution benefits resulting from interaction and collaboration of several aircraft. Given that some available high-fidelity simulations do not yet support multi-vehicle scenarios, the presented work introduces a framework which allows several individual single-vehicle simulations to be combined into a larger multi-vehicle scenario with little to no special requirements towards the single-vehicle systems. The created multi-vehicle system offers real-time software-in-the-loop simulations of swarms of vehicles across multiple hosts and enables a single operator to command and control a swarm of unmanned aircraft beyond line-of-sight in geometrically correct two-dimensional cluttered environments through a multi-hop network of data-relaying intermediaries. This dissertation presents the main aspects of the developed system: the underlying software framework and application programming interface, the utilized inter- and intra-system communication architecture, the graphical user interface, and implemented algorithms and operator aid heuristics to support the management and placement of the vehicles. The effectiveness of the aid heuristics is validated through a human subject study which showed that the provided operator support systems significantly improve the operators' performance in a simulated first responder scenario. The presented software is released under the Apache License 2.0 and, where non-open-source parts are used, software packages with free academic licenses have been chosen--resulting in a framework that is completely free for academic research.