Underwater gliders (UGs) are extensively used as efficient long-term ocean observation platforms and have evolved into cooperative observation networks. However, the related reviews remain at the individual-glider level, failing to capture this evolution because of the lack of a comprehensive fleet network. To address this gap, the present review summarizes recent progress in UG applications and assesses the trajectory of current research on UG fleet networks, categorizing fleet applications into ocean phenomenon observation and target detection. UG technologies involving coordination control, task allocation, path planning, and fleet communication are evaluated, shore-based control systems are described, and the potential of network formations is discussed. This work concludes with a discussion of challenges in UG utilization and offers guidance for future research on UG fleet deployment.