Two hundred meters underwater, a submarine has no windows, no stars, and no GPS the instant it submerges, every satellite the modern world relies on goes silent. So how does a machine cross an entire ocean, stay hidden for months, and still know exactly where it is? In this video we break down how submarines actually navigate without GPS: the inertial navigation system at the heart of every boat, why it slowly “drifts,” and the quiet toolkit subs use to correct course without ever surfacing Doppler velocity logs, maps of the seafloor, and navigation by the planet’s own gravity. We also get into why a submarine stays deliberately blind: when being invisible matters more than being connected, you don’t ask the sky where you are. You remember every move you’ve ever made. A look at one of the last great machines that can find its way across the world using nothing but what it carries inside

Source: How Submarines Navigate for Months With No GPS