On any given day the U.S. Navy has 100 ships deployed around the world — one third of its current fleet but that is much smaller than during the Reagan buildup in the '80s when the Navy had nearly 600 warships.

Today, deployments have grown long and frequent tax both crew and equipment as threats proliferate in the post-Cold War era.

That's why the new $715 billion Biden defense budget raised eyebrows among Republicans who complain it makes the U.S. vulnerable in a possible future war with China.

"I know our allies and the American public have to be very concerned that this administration believes that our military needs will be scaled down at a time where the threats are scaling up," said Rep. Mike Turner, R-Ohio, on Fox News’ "Sunday Morning Futures."

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"We need a Navy to grow with our focus on Asia, specifically China. We need to have more ships," said Roger Zakheim, director of the Reagan Institute. "China is now viewed as the U.S.'s greatest threat," according to a recent survey by the Reagan Institute.

The deputy defense secretary explained where the money is going.

"We lessened our reliance on vulnerable systems that are no longer suited for today's advanced threat environment or are too costly to sustain," said Kathleen Hicks Friday. "We reallocate resources to fund research and development in advanced technologies, such as microelectronics. This will provide the foundation for fielding a full range of needed capabilities, such as hypersonic missiles, artificial intelligence, and 5G."

The defense budget calls for $5.1 billion to be spent on a "Pacific Deterrence Initiative" to counter Beijing.

Defense Secretary Lloyd Austin said the budget had the "largest ever" increase in research and advanced weapons development. The White House proposed $112 billion for R&D, a 5% increase from last year.

In September, the Pentagon announced for the first time that China now has the largest Navy in the world. Some defense hawks questioned why Biden’s new defense budget Friday called for cuts to the number of warships.

The admiral in charge of the naval budget says he needs more new ships to grow the fleet to what the Navy believes is the right size.

"I would tell you that eight ships a year is not going to get to 355. And so all things being equal, if you have a 300-ship navy and a 30-year life, you have to recapitalize at 10 per year and so eight is not going to do it," the Navy’s top budget official, Rear Adm. John Gumbleton, said Friday.

"That said, we're consistent with last year's request of eight ships. We're requesting eight this year again," he added.

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Pentagon press secretary John Kirby said the Navy will not be cutting the fleet. "You’ll see more ships added," he said at a news conference Tuesday. Defense Secretary Austin also supports a 355-ship fleet, Kirby said.

Kirby said it’s important to have the "right mix" of warships and support vessels in the fleet.

"You could have a fleet of 355 tugboats," Kirby added. "But that doesn’t give you the kind of capabilities you’re going to need to defend this country."

Navy officials worry the pace of aircraft carrier deployments is breaking the fleet.

The USS Theodore Roosevelt just returned home to San Diego last week after making two deployments in one year.

Last week, the Pentagon ordered the Pacific-based aircraft carrier USS Ronald Reagan to deploy to the Middle East to relieve the USS Dwight D. Eisenhower, also on its second deployment in just one year. The lengthy deployment pushes the limits of the safe deployment of vessel's nuclear reactor, which officials say needs a complete overhaul making another extension out of the question to provide air support to the remaining U.S. troops leaving Afghanistan. Last August, the Eisenhower returned to Norfolk after a record 161 days at sea.

"We shouldn't have to make these choices as a superpower," Zakheim added. "We shouldn't have to make choices when it comes to stabilizing the Pacific as well as the Middle East."

There was a time when a nation's military strength was measured in battleships. That time is no more with the focus on cyber warfare, space and hypersonic missiles.

The Biden administration's budget request for shipbuilding is the same as President Trump's from last year.

The Trump administration’s last defense budget slashed shipbuilding by 20% compared to the previous year’s budget despite calls to grow the fleet to 355 ships over the next decade.

Overall, the Biden defense budget increased the Navy's budget by almost $4 billion.

"President Biden’s request for the Department of Defense is disappointing, dangerous, and a disservice to our men and women in uniform. At a time where the threats to U.S. security are rapidly increasing, we cannot underfund our military and ask them to ‘do more with less,’ as President Biden’s budget does," said Sen. Tommy Tuberville, R-Ala., in a statement.

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"From increasing spending to the highest levels since WWII to keeping the Pentagon’s budget near stagnant as our nation faces new threats around the globe, President Biden’s plan is radically out of touch with the American people," said Sen. Joni Ernst, R-Iowa, in a statement. "A near frozen defense budget will not satisfy the needs for the military to counter threats ranging from an emboldened China, a revanchist Russia, and constant bad actors such as Iran and North Korea."

"The President’s Defense Budget Request is an outline and a starting point," said Senate Armed Services Committee Chairman, Sen. Jack Reed, D-R.I. "Taxpayers shouldn’t have to pay for programs or systems that are wasteful and ineffective. And Congress must not shirk its responsibility to get rid of outdates weapons systems in favor of more advanced, effective new technologies and capabilities."