A sentinel from the 3d U.S. Infantry Regiment conducts the changing of the guard at the Tomb of the Unknown Soldier at Arlington National Cemetery, Arlington, Va. (U.S. Army photo by Elizabeth Fraser.)

We all know the United States is a formidable power, capable of unleashing its vast military strength against any enemy, at a moment’s notice, anywhere in the world.

But the world has changed.

Russia and China have both bolstered their military strength in vital sectors — the latter at an unprecedented rate.

Reflective of these changes, and according to a Heritage Foundation report, if the US wants to be ready to wage long-term war with foes like Russia and China, at the same time, it remains “underfunded.”

The report calls for more troops, planes ships and high-tech assets, claiming it is only about “two-thirds the size it should be,” writes Richard Sisk at Military.com.

This in a nation which is already recording record military budgets, in the range of US$740 billion.

“As currently postured, the US military is only marginally able to meet the demands of defending America’s vital national interests,” Heritage said in its annual Index of US Military Strength.

The foundation based its assessment “on the ability of America’s armed forces to engage and defeat two major competitors at roughly the same time,” and judged that the US military currently could handle only one major enemy, Military.com reported.

“It’s all about the money,” said Dakota Wood, a retired Marine lieutenant colonel and senior fellow at Heritage. “We have really under-invested over a number of years.”

The Heritage Index assessed US military strength across the service branches on a five-tiered scale of “very weak,” “weak,” “marginal,” “strong” and “very strong.”

The ratings for the Army, Air Force and Marine Corps were “marginal;” but the rating for the Navy was trending to “weak,” based on the number of ships, their age and the time it takes to produce more, Military.com reported.

Wood also described a sobering reality, on the naval situation vis-a-vis China.

Boatswain’s Mate Seaman Noah Canada, from Newnan, Ga., and Scott Rap, from San Diego, attach a cargo pendant on an MH-60R, Seahawk, assigned to Helicopter Maritime Strike Squadron 51, during a vertical replenishment test on the flight deck aboard the Ticonderoga-class guided-missile cruiser USS Shiloh. (U.S. Navy photo by Mass Communication Specialist Seaman Santiago Navarro.)

The Navy currently has roughly 300 ships, and “over half of those ships are more than 20 years old,” Wood said.

Of the 300, “only about 100 are available on a daily basis,” he said.

“Of those 100, perhaps 60 are deployed into the Western Pacific — so 60 US ships going up against a Chinese navy of 350 ships quickly growing to 400 in the next few years.”

Not only that, but an “incredible asymmetry” exists in the region due to the People’s Liberation Army Rocket Force.

According to Adm. Philip Davidson, who spoke at the Halifax International Security Forum this week, “China will test more missiles — conventional and nuclear associated missiles — this year than every other nation added together on the planet,” National Defense reported.

“They’re creating very advanced platforms — and weapons systems to go with those platforms — in the naval or maritime sphere, with their air forces [and] with their rocket forces,” he said.

“That presents a threat not only to its key security concerns along the border, but certainly along the whole First Island chain,” he said, referring to major archipelagoes out from the East Asian continental mainland coast.

Secretary of the Navy Kenneth Braithwaite, who also spoke at the Halifax Forum, said China has over the past decade pivoted to the seas and has had what he calls “an awakening.”

The People’s Republic of China “has seen that all great powers of the world have always been maritime nations,” he said.

“Prior to that they had been pretty much a land-centric military. Well, they no longer are land centric. As we speak today, they have more ships than any nation in the world.”

The US Navy is examining several different options as to how it could position itself in that part of the world, National Defense reported.

“There’s no ifs, ands or buts about it,” Braithwaite said.

“The United States is not looking for any type of confrontation. We are freedom loving people. But we want to make sure that those nations that align with our beliefs recognize that we are willing to protect their interests as well as our own, and that is through a freedom of navigation.”