A series of joint naval drills between the United States and France recently didn't quite turn out the way the US, no doubt, expected. The practice scenario ended with the French nuclear submarine that was acting the part of an enemy ship "sinking" the American aircraft carrier and most of its escort.

The exercises took place over 10 days starting in mid-February off the coast of Florida. The French nuclear attack submarine (SNA) — named Saphir — joined US Carrier Strike Group 12, comprising the aircraft carrier USS Theodore Roosevelt (nicknamed the "Big Stick"), several Ticonderoga cruisers or Arleigh Burke destroyers and a Los Angeles class nuclear attack submarine.

— Clifford Davis (@CliffDavisJax) January 27, 2015

The exercises were meant to test the newly upgraded carrier, which had undergone a four year, $2.6 billion overhaul, ahead of the Strike Group's deployment.

“We are going to experience real combat situations from all angles, there will be training evaluations from a hostile ship boarding, submarine attacks, and enemy ships or vessels trying impede their justice upon our strike group,” said Capt. Scott F. Robertson, of the USS Normandy in a statement about the exercises.

Better Friend Than Foe

And all those exercises went well while SNA Saphir was on the American side of the imaginary conflict, in which fictional states were attacking US economic and territorial interests. The French sub supported the American vessels in anti-submarine warfare drills.

However, the second phase of the exercises found the French ship playing on the enemy side, charged with a mission to find and attack the Theodore Roosevelt.

And so it did, sneaking deep into the defensive screen of the Strike Group, avoiding detection by the American anti-submarine warfare assets, and, on the last day of the drill, "sinking" the Roosevelt and most of it's escort.

Aircraft Carriers Iconic, but Vulnerable, Naval Giants

Aircraft carriers travel with these escorts, and train with submarines, precisely because they are so vulnerable to submarine attacks, the USS Theodore Roosevelt proving no (theoretical) exception.

"For every sailor who’s not in a submarine, submarines are real scary," writes David Axe at Real Clear Defense.

"Stealthy and heavily-armed, subs are by far the most powerful naval vessels in the world for full-scale warfare—and arguably the best way to sink those more obvious icons of naval power, aircraft carriers."

The original report on the drills was published March 4 on the website of the French marines under the headline, “Le SNA Saphir en entraînement avec l’US Navy au large de la Floride,” but has since been removed. A link in a Marine National tweet about the drill likewise, leads to a blank page. Parts of the article, however, are reproduced in French language reports.