by DAVID AXE

The U.S. Air Force quietly keeps a small, inconspicuous spy ship in the Persian Gulf, presumably in order to keep an eye on Iran’s missile launches.

Technically speaking, USNS Invincible—a 224-foot vessel displacing a mere 2,800 tons—belongs to Military Sealift Command, the quasi-civilian branch of the Navy that operates America’s military logistics ship and other specialist vessels.

But Invincible is just a hull—unremarkable, painted white and maintained by 18 civilian contractors. It’s what’s inside and atop the hull that really matters. A sophisticated, dual X- and S-band radar called Gray Star that belongs to the Air Force.

No one says much about Invincible or Gray Star. Military Sealift Command refers to the vessel as a “missile range instrumentation ship” whose job it is to “monitor missile launches and collect data.”

The Air Force’s Intelligence, Surveillance and Reconnaissance Agency, in its official history for 2012, lumps Gray Star in with its sea-based systems that collect “scientific and technical data of foreign military capabilities and systems.”

War Is Boring obtained a copy of the history through the Freedom of Information Act.

The word “Iran” does not appear in any official description of Invincible or Gray Star.

But it’s apparent from the ship’s deployments that she spends most of her time keeping tabs on the regime in Tehran—specifically, Iran’s expanding arsenal of medium-range ballistic missiles.

The Air Force ISR Agency admits that Invincible “typically” deploys to Central Command’s area, which includes the Persian Gulf and Indian Ocean. But there’s not a lot of actual evidence of the ship’s presence overseas. The military seems keen to downplay Invincible’s activities.

In May 2012, Invincible—which has no official home port in the U.S.—passed through the Strait of Hormuz into the Persian Gulf in a convoy of U.S. Navy and British vessels. An official photo depicts the transit.