When you want to send an international message that can’t be missed, you send an aircraft carrier. When you want to put up a neon sign, you send two. And yesterday, the U.S. Navy did just that, by confirming that the USS Carl Vinson and the USS Ronald Reagan carrier strike groups had joined up off the Korean coast.

It’s quite a statement—and in some ways a scary one, especially as it comes amid than the world has seen in years.

Just to stir the pot a bit more, two ships from the Japanese Maritime Self-Defense Forces (JMSDF) are sailing with the Vinson and Reagan as well, including the 19,000-ton mini-carrier, the JS Hyuga.

The two carriers have joined up in the Sea of Japan for a short window of dual-carrier operations before the Vinson breaks off and returns home to San Diego after being deployed since the beginning of January.

The USS Ronald Regan is the only forward deployed American aircraft carrier, calling Yokosuka Naval Base, Japan home. After the carrier’s extended maintenance period, pilots from Carrier Air Wing (CVW) 5 delivered over 70 aircraft to the Reagan as it sailed south of Japan. CVW-5 consists of seven squadrons, and one detachment of logistics aircraft, including the first Pacific deployment of the E-2D Advanced Hawkeye radar plane.

The latest iteration of the venerable airborne radar warning aircraft just arrived in January, to strengthen the capability of the Reagan’s air wing. The E-2D is the digital quarterback of the battlegroup, able to more effectively obtain and track targets than the old E-2C it’s replacing.

Each carrier strike group usually contains two destroyers (each with a 96-cell vertical launch missile system primarily used for cruise missiles and anti-air weaponry, plus myriad other Harpoon anti-ship missiles and torpedoes, so quadruple all that), one cruiser (equipped with a 122-cell vertical launch missile system of its own, so double that), and at least one attack submarine lurking nearby (so double that). Plus each carrier’s complement of up to 90 aircraft. Plus whatever the Japanese ships are packing.

It’s got a bit of punch, is what we’re saying.

Sure, the Navy will put forth the idea that American and Japanese naval vessels routinely operate and train together to improve their collective combat capabilities. Which is true, but it’s not often that mere training involves one-fifth of the American aircraft carrier inventory, and occurs close enough North Korea in the Sea of Japan, which is where most of North Korea’s missiles eventually land.

The United States only has 10 nuclear-powered aircraft carriers, and while operating two carriers together to conduct dual-carrier operations is not unprecedented, it doesn’t happen very often.

Despite an, the combination of two carrier battle groups has happened only three times over the last three years. Last year, the Reagan the USS John C Stennisin the Philippine Sea, and before that the last dual-carrier operations in the Pacific were in 2014. Even President Bill Clinton used two carriers to get the attention of China’s leaders in 1996, when he to the Taiwan Strait in response to Chinese missile tests.

China recently, and in the near future will be attempting to conduct dual-carrier operations of its own.

Despite the planned departure of the Vinson, the Ronald Reagan won’t be the only carrier in the Western Pacific for long. This week the USS Nimitz departed homeport in Bremerton, Wash. to begin its deployment. After a short visit to San Diego to pick up it’s air wing and final ships of its strike group, Nimitz will re-certify it’s air wing and begin the Pacific transit.

The Navy, as expected, isn’t commenting on whether or not the Nimitz plans to replace the Vinson, and continue the dual-carrier setup.