## 1 Introduction  
Remote robotic systems are increasingly becoming essential for industries hosting hazardous facilities for their personnel. The use of robotic systems could not only increase personnel safety but also improve the monitoring, inspection, and maintenance of environments to which access is constrained, limited in time, or not possible at all. Moreover, such robotic systems could be permanently installed in confined areas, improving the availability of the facility by removing the time necessary to access the area, which could be nonnegligible due to complex access procedures, remote locations, or a mandatory waiting period before ensuring safe human access. Underwater robotic interventions present similar issues. Particular tasks, such as wreck inspections and manipulation, are far too dangerous for humans and remote robotic systems are necessary to perform them safely. However, currently available robotic systems lack that level of usability necessary to broaden their use in both scenarios and require a pool of trained expert operators to ensure safe and successful operations in hazardous environments. Moreover, certain tasks may need a team of robots controlled with a certain degree of synchronisation, which is not easily achievable when multiple operators are involved. For example, picking up and transporting material is a common task, which requires big and delicate objects to be transported by multiple agents. The CERNTAURO project [1] aims at creating a complete system for remote interventions in the European Center for Nuclear Research (CERN)'s accelerator environments, including preparation, preliminary studies, safety, and execution of the tasks. For this purpose, a modular, usable, and multimodal human-robot interface was developed [2] to ensure easier and safer operation of multiple remote robotic systems. The CERNTAURO project tackled a series of recurrent tasks, proposing different robotic solutions to ensure their accomplishment. Among the identified tasks, those requiring the use of multiple robotic systems appeared to be the most complex ones. The TWINBOT project aims to go beyond the state-of-the-art in the field of underwater cooperative interventions. Common requirements and problems were identified with the CERNTAURO project, and the proposed Human-Robot Interface (HRI) with its functionalities was adapted and further developed to allow control of underwater vehicles. As a matter of fact, at the moment of writing, the TWINBOT project presented results in simulated scenarios for underwater mobile manipulators, including vision and underwater communications. Additional details about the TWINBOT project are available in Section 1.2. The CERNTAURO project is more mature, and at the moment of writing this paper, more than 100 real interventions in hazardous environments have already been performed, including some dual-arm and cooperative ones, especially thanks to the modular CERNBOT platform [3]. Moreover, some work has been done to solve the communication constraints found between the accelerators' underground tunnels and the operator location. Additional details of the CERNTAURO project are available in Section 1.1. In this paper, a solution to the problem of allowing a single operator to control multiple agents simultaneously is presented. The proposed solution makes use of behavioural control scripts programmed during the task preparation, customised and adapted during the task execution. Such scripts allow the creation of additional behaviours interconnecting multiple agents during the operation. The control scripts are executed on the human-robot interface, which can communicate with all the available agents seamlessly. The proposed solution satisfies the requirement of multiple agents controlling both the CERNTAURO and the TWINBOT projects. The CERNTAURO and TWINBOT projects are first introduced in more detail, highlighting their synergies as well. Then, the paper introduces the state-of-the-art of HRI for robot teams.