Somewhere in the depths of the Pacific Ocean, sometime in the last few weeks, the USS Jimmy Carter carried out an important mission for the nation. It was probably related to spying.

Here's what we know. On Tuesday, a sharp eyed journalist, Ian Keddie, noted that the Seawolf-class attack submarine, USS Jimmy Carter, had returned to its Washington port while flying the Jolly Roger pirate flag. The Navy, whether by accident or by design, published the photo online.



The Jolly Roger's significance is its celebration of a successful operation in face of the enemy. As an attack submarine, the on-paper primary mission of Jimmy Carter is finding and destroying enemy vessels. Yet since the end of the cold war, the Seawolf has been repurposed as an undersea intelligence gathering machine.

As Joseph Trevithick noted in a 2016 article for War is Boring, the USS Jimmy Carter received a presidential unit citation for an operation in 2013. That means it did something very important and very dangerous. We don't know what that something was, but Trevithick convincingly argues that it was very likely related to intelligence gathering.

I strongly suspect the same is true of Carter's most recent mission that earned the Jolly Roger. As my map below shows, there are numerous high-value target areas in reach of Carter's home port. The red line leads to the Arctic, where Russian submarines like to hang around. The grey line leads to the Pacific Fleet headquarters of the Russian navy. The green line leads to waters off North Korea, and close to most of its missile launching sites. The purple line leads to China.



But what might the latest Jolly Roger effort have entailed?

A few things.

First, the Carter could have been employed to tap into undersea fiber-optic cables used for communications by adversary states like China, North Korea, and Russia. This is difficult work, like balancing an invisible needle at the bottom of an ocean haystack.

Alternatively, perhaps the Carter was gathering intelligence on the disposition and capabilities of Chinese, North Korean, or Russian military vessels and ports. This intelligence can be used to help plan future operations, and to ensure the U.S. is ready for any surprises those nations might be preparing. This, of course, is nothing new. As Sherry Sontag outlined in her excellent book, Blind Man's Bluff, submarine-based espionage was a critical tool of U.S. intelligence for the duration of the Cold War. And as I noted last month, North Korea's submarine capabilities are advancing. Perhaps the Carter was seeing just how far they've come?

Or seeing as it is designed to insert special operations forces, maybe the Carter was infiltrating or exfiltrating personnel onto or from foreign soil. Such capabilities extend a submarine's utility to ground operations deep into enemy territory. That matters, because for all the power of spy satellites and cyber-espionage, there is a range of specific intelligence missions that necessitate boots on the ground. Sending a silent submarine a few miles off the coast and then having Navy SEALs swim ashore is sometimes less risky than infiltrating over land.

Ultimately, it's impossible to say what the Jimmy Carter has been up to. Still, we are lucky her crew is on our side.