sions [8]. The integration of robust communication technologies further ensures seamless coordination with remote operators and other autonomous systems.  
Despite their many advantages, USVs face several challenges that hinder their widespread adoption [4]. Regulatory frameworks governing autonomous maritime operations vary significantly across different regions, creating legal and logistical barriers. Furthermore, AI-driven autonomy is still evolving, with limitations in decision-making under unpredictable environmental conditions [9]. The need for robust cybersecurity measures is also a pressing concern, as USVs rely on remote communication networks that could be vulnerable to cyberthreats [10]. Addressing these challenges is essential for ensuring the safe and efficient operation of USVs in both commercial and defense applications.  
Concerning related works, the work from [PERSON] [11] provides a review on the general development of USVs, encompassing research prototype, developmental trends, and potential applications. In the work from [PERSON] et al. [4], the authors present a synthesis of 15 years of USV-related literature. Their work evaluates drivers, applications, and operational applications of USVs in a qualitative and quantitative way, assessing the necessary innovations that will enable the diffusion of the USV technology. Lastly, the authors argue that the functionalities of USVs are complementary of those traditional methods for ocean monitoring, challenging the perspective that USVs are replacing crewed ships. [PERSON] et al. [1] carried out a bibliometric analysis and overall review of the new technology and development of USVs, covering the literature from 2000 to 2023. Based on their analysis, the authors proposed six future research directions: (1) enhanced intelligence and autonomy, (2) highly integrated sensor systems and multi-modal task execution, (3) extended endurance and resilience, (4) satellite communication and inter-connectivity, (5) eco-friendly and sustainable practices, and (6) safety and defense. The review from [PERSON] et al. [3] evaluated existing applications and models of unmanned vessels. The authors concluded that the current maritime regulations, designed for crewed ships, did not entirely meet the profile of unmanned vessels. Also, they noticed that while small USVs were used for data collection, large USVs were still in the development stage. Other very interesting review studies have focused in related aspects of USVs, such as Guidance, Navigation, and Control (GNC) [12], path planning [13; 14], intelligent motion control [15], hull design [16], and Model-Free Adaptive Control (MFAC) [17].  
Therefore, different from previous works, this paper provides a comprehensive review of operative USVs, examining their technological evolution, design characteristics, and operational applications. Considering the USVs' capabilities, endurance, and intended use, this study highlights the key trends that have shaped the development of these systems. Through an analysis of existing platforms and market trends, this review aims to offer valuable insights into the current and future landscape of USVs.  
The rest of this paper is structured as follows. The next section (Section 2) presents a brief background of USV technology, covering its evolution, regulatory challenges, classification, key components, and applications. Section 3 discusses the operational trends and brings insights based on data from operative state-of-the-art USVs. Conclusions are given in Section 4.