China is busy pouring silt and building bases onto man-made islands in the South China Sea. Russia is launching newer, faster, quieter nuclear submarines. Iran is making noises about closing the Strait of Hormuz to U.S. shipping.

Throw in cyberattacks, piracy, smuggling of drugs, guns and people, and new technologies that are eroding America's traditional maritime superiority, and there is no lack of threats for the chief of naval operations to worry about.

"For the first time for what I would say is roughly 25 years, the United States is back to an era of great power competition," Adm. John Richardson told the National Press Club in January.

Richardson was a junior officer when the the Soviet Union collapsed, and spent his early years serving in a Navy where sailors listened to cassettes on a Walkman, a time, he says, when the U.S. was not significantly challenged at sea.

"That era is over," he said. "Both Russia and China have advanced their military capabilities to act as global powers again. Their goals are backed by a growing arsenal of high-end warfighting capability."

Today's U.S. Navy is facing unprecedented challenges, not only from a resurgent Russia and a rising China, but also from an emboldened Iranian regime flush with cash and freed from sanctions, and a bellicose North Korean leader who thumbs his nose at the international community.

But while threats from other nations have been a perennial menace, one word encapsulates the biggest future challenge: technology.

Not just the rapid development of new technologies, but the even faster rate at which those technologies are adopted and then adapted to military purposes.

Take for example, submarines.

"Our principal advantage for decades in this world has been that our boats were effectively invisible. That is an assumption we are not going to be able to consistently make going forward," warned retired Adm. James Stavridis, the former NATO supreme allied commander and current dean of the Fletcher School at Tufts University.

"Technology is increasingly favoring detection, and therefore over time our advantage is going to decrement. It's not going to suddenly go away. We're not going to suddenly fall over a cliff and find ourselves with transparent oceans. But it's trending in the wrong direction."

The trend Stavridis sees is a marriage of better optical and acoustic sensors to high-powered data processing, enabling ways to isolate tiny anomalies that can be identified as a submarine.

"It has not happened yet, but over time it will be easier to penetrate the ocean, particularly the deep ocean, where our boats historically had enormous advantage," Stavridis said.

Another area where Stavridis sees the U.S. losing its technical edge is cruise missiles. The offensive capability of cruise missiles is increasing, while the ability to defend against them in decreasing.

The effect of the technological tidal wave is not lost on Richardson, who has issued commander's guidance calling on everyone in the chain of command to learn faster and adapt faster.

"We must speed up," Richardson said in January. "The margins of victory in this environment are razor thin, but they are absolutely decisive ... This is truly a game of inches."

Richardson argues the key to keeping the U.S. Navy ahead of its competitors is people, and he says he's committed to making Navy careers inviting enough to attract the kind of tech-savvy workforce that can leverage technologies in creative ways.

But former Navy Secretary Gordon England warns that while people are part of the solution, manpower could also be one of the problems in the very near future.

"I was as at a National Academy meeting a couple of weeks ago and the fellow said the first person who will live to be 150 years old has already been born," England told the Washington Examiner.

"Think about it. That person has already been born, in 17 years they join the Navy or the military, and they retire at 38 years old, and then they are retired for 112 years at full benefits."

England sees the looming benefits bubble as the biggest future threat facing the Navy, a threat he says no one is talking about.

"With all these medical breakthroughs and everything going on that human life could be extended 10 years, 15, 20 years, I mean there's no way this works. I mean it's impossible. DoD can't possible have all these people retire."

And because trimming military benefits or reforming retirement is politically out of the question, England is also looking to technology for answers.

"You can't deal with this politically, so deal with it technically, and you're just going to have to find ways to replace people," England said. "I think you have to have far more automated and robotic systems."

Unless the Navy, and the U.S. military as a whole, begins to address the benefits bow wave, England argues, the rest of the debate becomes moot: "Frankly I think if you don't address that issue, you're not going to be able to defeat any threats going forward. We're just not going to have the capability. So I think that overrides everything."