It’s the middle of the night in April 2023 in the East China Sea.A North Korean-linked oil tanker sailing under another country’s flag suddenly goes dark. It stops transmitting its location using the Automatic Identification System (AIS) machine that all large commercial ships have on board. It simply vanishes from the map. Ten days later, the ship reappears on global tracking screens. Its signal places it off the coast of southern China.Except it’s not. It’s actually in a bay many hundreds of kilometres away, preparing to deliver oil to North Korea in violation of UN sanctions.Justin Hastings, a professor of international relations at the University of Sydney, has been tracking North Korea’s shadow fleets as part of his research. He describes to The Conversation Weekly podcast the tactics that North Korea uses to disguise the identities of its shadow ships – and why it has got away with it for so long.The first reason is that the oceans are a lot bigger than you think. It’s a lot harder to find ships that don’t want to be found in the ocean.The second reason is that there is this presumption under international law that if a ship is on the high seas, you won’t really interfere with it unless you have very specific legal reasons.Hastings compares the world’s oceans to the “Wild West” and says other countries such as Russia and Iran have now borrowed from North Korea’s playbook.For countries that are engaging in sort of large-scale campaigns to evade sanctions, like Russia, that also have lots of money and lots of ships, boarding the ships […] is one way to at least slow them down.But obviously there’s a lot of ships and every interdiction is really expensive and potentially dangerous.Disclosure statement and creditsJustin Hastings does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.Newsclips in this episode from BBC News and The Wall Street Journal. This episode of The Conversation Weekly was written Justin Bergman and produced by Isabella Podwinski. Mixing by Lloyd Barrett and theme music by Neeta Sarl.Justin Bergman does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.