The Deep Sea Bumper Car Incident: How Japan’s JS Soryu Learned the Hard Way About Underwater Traffic

4 min readOct 11, 2024

Alright, folks, let’s talk about the latest episode of “Why Underwater Joyrides Can Go Horribly Wrong.” On February 8, 2021, a Japanese Maritime Self-Defense Force submarine — the JS Soryu — decided to get up close and personal with a Hong Kong-registered bulk carrier, the Ocean Artemis, off Japan’s Shikoku coast. Yeah, that’s right — a 275-foot-long, multi-million-dollar military submarine collided with a massive cargo ship. And why? Because navigating underwater in a crowded ocean apparently makes a game of bumper cars look like a peaceful afternoon tea.

So here’s how it went down. The Soryu was surfacing as part of a training exercise about 40 kilometers southeast of Cape Ashizuri. Picture it — sun shining, seas calm, and a 2,900-ton submarine saying, “Hey, I think I’ll poke my head up!” Now, in submarine lingo, they call this maneuver the “baffle clear.” That’s when they do a little swerve to make sure nothing’s hanging out in their blind spot, which is conveniently right behind them — a whole section where sonar goes, “Eh, I’m not sure.” But when you’ve got cargo ships bigger than football fields hauling through at 20 knots, time is not your friend. You’re pretty much banking on the hope that everything else gets out of your way.

Now, let’s add a little wrinkle called the Kuroshio Current — think of it as Japan’s version of the Gulf Stream. It’s a warm ocean current that slides up Japan’s coast, and it loves to create these underwater thermal layers. Why is that important? Because thermal layers bend sound waves, and all that fancy sonar tech on submarines doesn’t work so well when sound is busy taking the scenic route. So, if the Ocean Artemis’s bow quietly slid through this thermal layer first, the Soryu might not have heard it coming. I mean, it’s like relying on noise-canceling headphones and then wondering why you didn’t hear the 18-wheeler about to flatten you.

And here’s the kicker — this all happened in broad daylight! That’s right, no stormy weather or dark night to blame. But remember, submariners are human too. You’ve got a crew that’s probably tired, maybe a little overconfident from all that deep-water training. Now they’re in shallow water, thinking they know the game. But ocean currents don’t play by the same rules as the quiet waters of the Pacific depths. Those currents can mess with sonar readings, and suddenly, that big echo from the cargo ship could be mistaken for anything from a distant ship to a playful school of fish.

In the aftermath, Japan’s military is likely scratching their heads and rewriting a few rulebooks. I mean, this is a $500 million sub they’re talking about.

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