Why might a navigator use dead reckoning?

A navigator might use dead reckoning when GPS systems are unavailable because this method allows them to determine their current position based on a previously known location, taking into account the speed and direction of travel over time. Dead reckoning involves estimating one's position by using the course, speed, and time traveled from the last known position, which makes it a vital skill in situations where electronic navigation aids are inoperable or unreliable. This method has been used historically and remains crucial for navigators in maritime and aviation contexts to maintain situational awareness and ensure safe navigation. It is particularly useful when in open waters or in environments where visibility is limited and GPS signals may not be accessible.