## 2 Brief Background of USV Technology
### Regulatory Challenges  
Concerning regulatory challenges faced by USVs, an Herculean effort has be made over the last years to develop international and national legal frameworks. However, most of the development of Maritime Autonomous Surface Ships (MASSs) has been carried out using a human-centric approach [24], assuming the presence of humans for navigation, monitoring, maintenance, and emergency handling, which poses gaps and uncertainties when, for instance, vessels without crew or remotely operated are considered. The work from [PERSON] et al. [25] identified that a significant portion of these gaps related to core conventions like SOLAS (62%), COLREG (12%), STCW (6%), and ICLL (5%).  
In addition to the human-centric approach issue, which poses direct challenges to crewless operations, there exist ambiguities of key terms like master and crew in the context of unmanned vessels, impacting compliance with various regulations and international legal instruments like UNCLOS (United Nations Convention on the Law of the Sea). Another point regards the regulations specifically for autonomous operations, which creates uncertainty for stakeholders for design, testing, and operational standards. All these challenges and uncertainties impact negatively on the growth in investment and development in this field. Thus, to overcome these barriers, some solutions were proposed [25]: redefining roles and responsibilities, such as designating remote operators as equivalent to the \"master\" or \"crew\"; the IMO MASS code, which is a significant step towards establishing internationally accepted guidelines; and international collaboration for ensuring the safe and efficient cross-border operation and wide acceptance of MASSs.  
Many authors have been studying regulatory and legal frameworks related to MASSs. The article from [PERSON] [26] gives an overview of the revolutionary potential regardingunmanned vessels. Through the exploration of regulatory challenges associated with international regulations and the implementation of USVs, the author discusses how existing international maritime laws and conventions need to adapt to accommodate the innovations brought by USV technologies. [PERSON] (2017) and [PERSON] et al. (2018) analyzed the international legal status of different types of MASSs from the perspective of the law of the sea (UNCLOS), where the first work analyzed the relevance of existing laws, necessary amendments, and development of new rules, and the second one suggested responsive measures for how coastal states manage foreign USVs operating in their waters. The work from [PERSON] et al. (2015) focused on the regulatory and legal challenges posed by MASSs in short sea shipping. The gaps found in different international and national frameworks were classified by severity; then, the authors proposed recommendations to fill these gaps. Also, an important point is that in their analysis, the work from [PERSON] et al. took into account the different levels of autonomy, creating a clear structure for policymakers.  
Finally, on the subject of regulatory development through the globe, Europe seems to be at the forefront of actively addressing the regulatory challenges of autonomous vessels, particularly within its regional and national frameworks. On the other hand, while many nations recognize the need for international regulations, information regarding the advancements in Asia, Africa, North America, South America, and Australia are more limited, but the few existing ones suggest that these regions are actively examining the implications of maritime autonomous technology and considering their national and local regulations as basis for MASS-related regulations.