Catastrophes happen worldwide, in some areas more often than in others. The first priority is to circumvent these catastrophes. When a catastrophe is not preventable or out of human influence, preparations need to be made. Not only are materials reserves and structural measures required, but also the personnel in the disaster relief management needs to be prepared. The squad leaders, in particular, have to be prepared, to make the right decisions, which influence the outcome of the relief operation tremendously. Therefore, the squad leaders need to be either experienced or are well trained. However, to effectively train squad leader, simulation exercises need to be executed to compensate the experience gap. To arrange large simulation exercises, many relief units, a lot of materials, a suitable location, and role play actors are required. Additionally, the government and the local communities must endorse ambitious simulations. In order to create an alternative to real simulation exercises, the FFG funded project, "VROnSite" was started in the year 2015. The aim of this project was to develop and evaluate the first fully mobile, generic, multi-user immersive virtual reality platform to train squad leaders of first responder units, such as fire brigades, paramedics, police forces and other disaster relief units. The goal of this master thesis was to extend the VROnSite project by developing a distributed 3D interaction system to allow for immersive training of multiple first responders, supervised by a trainer, within a virtual reality environment. For the visualization part of the scenario, mobile head-mounted displays are used. To navigate through and interact within the virtual reality, gamepads and omnidirectional treadmills are used. To make the system able to perform the training simulation with multiple users, a distributed layer had to be integrated. The main intention of the system is to train squad leaders upon arrival at the disaster site. To enable simulation and training of the entire command cycle, distributed 3D interactions are going to be developed, including 3D selection and manipulation tasks employed by the participants within the immersive simulation, and 3D manipulation tasks by the trainer, using desktop input. The innovative modules will be tested with actual stakeholders, such as fire brigade and paramedic training centers.