Navy and Marine leaders need to take a fresh look at the branches' future roles and resource requirements, U. S. Defense Secretary Robert Gates said on Monday.

For example, while the Defense Department currently plans to maintain 11 carrier strike groups through 2040, Navy leaders should question whether that strength level will be warranted in coming years, Gates said. Likewise, Marine Corps leaders should think about whether Marines will ever launch another major amphibious landing, he further added.

The Armed Forces Press Service reported that speaking to Marine and Navy officers and defense contractors at the Navy League's annual Sea-Air-Space Convention at the Gaylord National Convention Center in Maryland, Gates said the world is changing and the nation's oceangoing military services need to adapt.

According to Gates, by one recent estimate the Navy's battle fleet is larger than the next 13 navies combined, 11 of which are allies or partners. The country's 202,000-strong Marine Corps is bigger than most nations' armies, he added.

He also said that rather than going head-to-head against other major powers, the United States is more likely to need innovative strategies to battle terrorists and nations that don't fight in conventional ways, and more sophisticated underwater combat systems.

In the past the debate has usually been whether to add "either more of what we already have or modernized versions of pre-existing capabilities," he said.

He further said, "This approach ignores the fact that we face diverse adversaries with finite resources that consequently force them to come at the U. S. in unconventional and innovative ways. The more relevant gap we risk creating is one between the capabilities we are pursuing and those that are actually needed in the real world of tomorrow." (With Inputs from Agencies)