Submarine operations represent one of the most demanding environments for resilient timing. With no access to GNSS for weeks or months, maintaining nanosecond-level accuracy is critical for secure communications, navigation, and mission coordination, as well as for enabling rapid and accurate GNSS reacquisition once even limited signals become available. The extreme denial durations place unique demands on oscillator stability. These challenges call for innovative solutions that combine high-stability hardware with advanced algorithms to predict, correct, and minimize accumulated timing deviations, as well as fast acquisition. This session will explore the unique timing challenges of submerged platforms and present approaches to extend ePRTC-class performance into truly denied and mobile environments. We will highlight application needs from a defense perspective and then examine algorithmic techniques and simulations that mitigate timing deviation and enhance long-term holdover. The talk will combine operational context with technical solutions, offering fresh insight into timing resilience for critical defense missions.