Primarily, the compass was used for geomancy for a long time before it was used for navigation Ancient Chinese alchemists realized that the magnetite ore would point towards a magnetic north. Their ...

The earliest known compasses were made in China’s Han Dynasty ... the needle on your compass should still be able to register Earth’s magnetic field and point you toward that spot in Canada.

While no single technology guarantees sub detection, China is weaving magnetic tracking into a broader "kill web" that includes acoustic arrays, satellites, drones and AI algorithms to fuse data ...