The Navy could potentially get by with fewer ships if some of the larger, more capable unmanned vehicles could someday reliably do some of the easier missions ships do, but it's not a one-for-one replacement, said Bryan Clark, a senior fellow at the Center for Strategic and Budgetary Assessments.
An unmanned vehicle could lay mines and conduct surveillance but it couldn't board a pirate ship or help train a foreign Navy, added Clark, the lead author on a paper about the Navy's future force.
"It doesn't mean you buy an extra-large unmanned undersea vehicle and buy one less submarine," he said. "You have to figure out to what degree it replaces a submarine and do the math."