## 4 Results
### Research Questions Results  
In this subsection, the results for the development of the three research questions are presented, which are based on the information obtained from the papers labeled in the database according to the study categories. To address research questions 1 and 2, we analyzed all labeled articles. For research question 3, given the specific selection criteria related to USV autonomy algorithms, the analysis was centered on the selected articles. This focused approach allowed us to identify the different approaches used in studies within the GNC architecture framework. 2.1 What Has Been the Evolution of Studies on USV Regarding the Applications and the Achievement of Autonomous Capabilities? The results obtained show that the topic is relatively recent. The first documents in the databases are recorded from the year 2004. Starting in the year 2015, they began to increase significantly, and most of the production has occurred in the last 5 years (2019-2024) with 54.43% of the total as shown in Figure 3. The trend is expected to continue in 2024. The produced documents have been published through various sources, as shown in Figure 4. Initially, the journal dedicated to strategic and military security issues, _Jane's Defence Weekly_, was the only one; in 2007, production on this topic ceased. Subsequently, in 2010, _The IEEE International Conference of Intelligent Robots and Systems_, a journal on robotics, began publishing and has since maintained relevance, with a higher cumulative total compared to the rest, along with _Ocean Engineering_, which is dedicated to research and development in naval engineering. Based on this, it is pertinent to appreciate that unmanned vehicles encompass a broad scope of interest that includes the naval industry, intelligent systems, and strategic military purposes. The thematic evolution confirms the aforementioned. Figure 5 shows that initially, the trending topic was military operations. Subsequently, hulls, navigation systems, and unmanned vehicles gained relevance along with the introduction of the term \"ocean engineering\" to categorize the research carried out in this field. Since 2008, remotely operated vehicles have maintained their presence in the thematic, alluding to the importance of these vehicles being able to operate without an onboard crew. For the years 2011-2015, robotics in this area began to be discussed as well as oceanography and autonomous navigation. Finally, for the years 2015-2017, the term \"unmanned surface vehicles/vessels\" was introduced, and with it, terms such as \"obstacle avoidance\", \"maneuverability\", \"object detection\", \"controllers\", and others, indicating evidence of the growing interest in achieving autonomy in these vehicles through navigation and control technologies. Figure 3: Production of documents over time. The evolution of academic production, considering the document type, shows an increasing trend in the number of articles, both journal and conference papers, with a more pronounced growth starting from 2010. Figure 6 shows the chronological evolution of the quantity of journal and conference articles. It can be observed that in most years, more conference papers have been published than journal articles. Additionally, fluctuations in both cases are evident. In this systematic review, starting from the screening stage, according to the document type, 206 conference papers, 150 journal articles, 2 book chapters, and 1 editorial were used. Figure 4: Production from the most relevant sources over time. Figure 5: Most relevant topics over the years. 2.2 What Are the General Areas in the Civil and Military Environments Where Unmanned Surface Vehicles Are Used? Hydrodynamic modeling technology and marine vehicle control systems have progressed significantly in recent years. In particular, USVs have found a number of fields where their application is highly useful [18].