Diesel submarines are a carrier commander's worst nightmare. More than 39 nations possess them.
"The beauty about a diesel submarine is that it has the potential to be far quieter than a nuclear submarine," says Guy Stitt, the president of AMI International, the US naval market analysts.
That makes them almost impossible to detect, and the Americans are worried.
"Our future adversaries are developing a set of capabilities specifically for the purpose of attacking our aircraft carriers," says Mark Gunzinger, a senior fellow with the US think tank the Center for Strategic and Budgetary Assessments.
Diesel subs are also cheap. The Russians have sold some of theirs for as little as US$200 million (Dh734.6m) and the French have exported their Scorpene class for $300m. The Chinese have 22.
"It is within the scope of many, many countries to be able to afford them. They don't need a lot of them.
"They don't need to sail them very far, and they don't have to be particularly proficient with them," says Admiral Samuel Locklear, of the US Navy.
"We know that [the Chinese] are continually expanding their reach in what they view as their own areas of interest and that their submarine force is vital to expanding that reach," he says.
"There's a wide array of military assets you can buy, so why would you buy a diesel-electric submarine? As far as I know, it's not to protect your own port."
With the proliferation of drones and satellite imagery, carriers become easier to locate and more vulnerable.
That means they "may not be able to get close enough to a future enemy that has precision-guided anti-ship cruise and ballistic missiles", adds Mr Gunzinger.
China's DF-21 anti-ship missile could force an enemy's carriers to operate more than 1,800 kilometres from its coastline.
But carrier-based jets with a heavy weapons load only have a strike range of 555km without refuelling.
It's a compelling dilemma that is prompting some very deep thinking.