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How does inertial guidance track a ship’s movement without using radar or satellites?

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An inertial guidance system tracks a ship’s movement by functioning as a sophisticated dead reckoning device that operates independently of external signals like radar or satellites.1

The system relies on three primary components: gyroscopes, accelerometers, and a computer. The process works as follows:2

Measurement: The gyroscopes establish a stable frame of reference or sense turning rates, while the accelerometers measure the craft's acceleration in three dimensions.21
Integration: Because acceleration is the rate of change of velocity, and velocity is the rate of change of position, the computer performs two successive numerical integrations on the data.21
Calculation: By integrating the acceleration data, the system determines the ship's current velocity; by integrating that velocity, it calculates the ship's current position relative to a known starting point.23

While highly effective for vessels like submarines, these systems are subject to cumulative errors over time and must be periodically reinitialized using independent navigation sources to maintain high precision.21