What principle does inertial navigation primarily rely on?

Inertial navigation primarily relies on the measurement of acceleration or displacement because it uses inertial sensors to detect changes in motion. These sensors track the object's acceleration over time, allowing the system to calculate the current velocity and position based on the initial state of motion. By integrating the measured acceleration, inertial navigation systems can derive displacement, which leads to determining the current position without needing external references. This method is particularly valuable in environments where GPS or other navigational aids may not be available, enabling the navigation system to function autonomously.