President Trump has proposed a $54 billion increase in defense spending, which he said would be “one of the largest increases in national defense spending in American history.”

U.S. defense spending 1981 Reagan 1989 Bush 1993 Clinton 2001 Bush 2009 Obama Trump’s 2018 proposal $700 billion Supplemental war funding 500 300 100 2009 Obama 1989 Bush 2001 Bush Trump’s 2018 proposal 1981 Reagan 1993 Clinton $700 billion Supplemental war funding 500 300 100 Source: Center for Strategic and Budgetary Assessments (in 2017 dollars)

Past administrations have increased military spending, but typically to fulfill a specific mission. Jimmy Carter expanded operations in the Persian Gulf. Ronald Reagan pursued an arms race with the Soviet Union, and George W. Bush waged wars in Iraq and Afghanistan.

Mr. Trump has not articulated a new mission that would require a military spending increase. This has left analysts wondering what goals he has in mind. Erin M. Simpson, a national security consultant, called Mr. Trump’s plans “a budget in search of a strategy.”

Military spending by country Proposed increase +$54 billion Russia 66 Britain 55 United States $596 billion France 51 China 215 Japan 41 Saudi Arabia 87 India 51 Russia 66 Britain 55 United States $596 billion China 215 France 51 Japan 41 Saudi Arabia 87 India 51 Proposed increase +$54 billion Russia 66 Britain 55 United States $596 billion China 215 France 51 Japan 41 Saudi Arabia 87 India 51 Proposed increase +$54 billion

United States $596 billion Next 7 countries 567 Rest of the world 514 Totals may not add up due to rounding. | Source: Stockholm International Peace Research Institute (2015)

The United States has higher military spending than any other country partly because its foreign policy goals are more ambitious: defending its borders, upholding international order and promoting American interests abroad.

“Our current strategy is based around us being a superpower in Europe, the Middle East and Asia-Pacific,” said Todd Harrison, the director of defense budget analysis at the Center for Strategic and International Studies in Washington. “We’ve sized our military to be able to fight more than one conflict at a time in those regions.”

Some of Mr. Trump’s statements have suggested a reduced footprint for the United States military.

He criticized America’s role as a global military stabilizer. Last month, in his first address to a joint session of Congress, he said the United States had “defended the borders of other nations while leaving our own borders wide open.”

He also called for defusing tensions with Russia, the United States’ chief military competitor.

But Mr. Trump has also taken positions that point to a more aggressive military posture.

He has advocated challenging China and Iran more directly.

He wrote on Twitter that America must “greatly strengthen and expand its nuclear capability.”

These statements have left analysts unsure about the role Mr. Trump wants the United States military to play in the world.

The following is a closer look at Mr. Trump’s proposed upgrades to four crucial aspects of the military — troops, air power, naval power and nuclear weapons — and what his new spending might achieve.

1 Troops

The United States has approximately 1.3 million active-duty troops, with another 865,000 in reserve, one of the largest fighting forces of any country.

Largest active armed forces China 2.2 India 1.4 U.S. 1.3 million troops North Korea 1.2 Russia 0.8 Pakistan 0.7 South Korea 0.6 Iran 0.5 Source: International Institute for Strategic Studies

The United States also has a global presence unlike any other nation, with about 200,000 active troops deployed in more than 170 countries.

Active American forces deployed outside the contiguous U.S. South Korea 23,468 Germany 34,805 Japan 39,345 Britain 8,479 Italy 12,102 Afghanistan 9,294 Pacific Ocean Germany 34,805 Britain 8,479 South Korea 23,468 Japan 39,345 Italy 12,102 Pacific Ocean Afghanistan 9,294 Afghanistan 9,294 Germany 34,805 South Korea 23,468 Japan 39,345 Britain 8,479 Italy 12,102 Pacific Ocean Afghanistan 9,294 Includes Army, Navy, Marine Corps, Air Force and Coast Guard. | Source: Defense Manpower Data Center

Many are stationed in allied nations in Europe and northeastern Asia. Mr. Trump has criticized these alliances, saying the United States does too much to defend its allies. It seems unlikely, then, that Mr. Trump intends his spending increase to bolster those deployments.

“The general concept of readiness often happens without a conversation about what the forces are for,” said Benjamin H. Friedman, a research fellow at the libertarian Cato Institute in Washington. “They don’t know exactly what they want to do, except that they want a bigger military.”

Mr. Trump wants to increase the number of active-duty military personnel in the Army and Marine Corps by about 70,000 — a rise of about 11 percent over the current total of 660,000.

Number of active Army troops and Marines U.S. involvement in the Vietnam War President Trump’s proposal Marines 1.5 million Army Iraq war 1.0 0.5 1956 1966 1976 1986 1996 2006 2016 U.S. involvement in the Vietnam War President Trump’s proposal 1.5 million Marines Army Iraq war 1.0 0.5 1956 1966 1976 1986 1996 2006 2016 Source: Defense Manpower Data Center

The United States increased troop levels in the early 2000s for the wars in Afghanistan and Iraq, but has scaled down as it has withdrawn from those conflicts. Mr. Trump has been critical of those missions, suggesting that he does not plan to ramp up operations in either conflict.

Gordon Adams, a former senior White House national security budget officer, said, “Unless you decide you’re going to war — and going to war soon — nobody keeps a large military.”

2 Air Power

The United States has around 2,200 fighter jets, including about 1,400 operated by the Air Force. Mr. Trump wants to add at least 100 more fighter aircraft to the Air Force.

Air Force fighter aircraft by generation 2nd gen. 2nd generation 3rd gen. 3rd generation 4th gen. 4th generation 5th gen. 5th generation U.S. 1,226 1,226 193 Russia 275 275 855 855 1 China 484 484 509 509 India 245 214 214 311 311 France 259 259 Japan 217 217 Britain 146 146 1 Includes only active and non-training aircraft. | Source: FlightGlobal and Teal Group

Analysts informally categorize fighter aircraft by “generations” as a way to compare capabilities. While there is some variation among analysts on how planes are classified, there is a broad consensus that American aircraft are more advanced than those of other nations.

While Mr. Trump has focused on the overall number of aircraft, this is an imperfect metric for either air power or cost.

The military already has plans to spend an estimated $400 billion on new F-35 fighter jets, a fifth-generation plane. But Mr. Trump has not provided any details on which programs he would expand.

Because different warplanes serve different roles at different costs, it is difficult to know what problem Mr. Trump is trying to address by adding 100 fighter aircraft.

3 Naval Power

The United States Navy has 275 surface ships and submarines. Mr. Trump wants to increase that number to 350, including two new aircraft carriers.

The new carriers would add to America’s already overwhelming advantage: More than half of the world’s 18 active aircraft carriers are in the United States Navy.

The world’s 18 active aircraft carriers, by country United States 10 supercarriers Trump’s proposal +2 Italy 2 China France India Russia Spain Thailand United States 10 supercarriers Trump’s proposal +2 Italy 2 China France India Russia Spain Thailand Trump’s proposal +2 United States 10 supercarriers Italy 2 China France India Russia Spain Thailand Source: International Institute for Strategic Studies

In early March, Mr. Trump said that the United States Navy was the smallest it had been since World War I.

Most analysts reject this comparison. Technological advances mean that individual ships are far more powerful and versatile than they were a century ago, allowing a single ship to fulfill capabilities that would have once required several ships.

Mr. Trump has not specified new missions that would require additional carriers, which could take years and billions of dollars to build.

Size of principal naval vessel fleets Cruisers, frigates, destroyers Subs* Submarines* Amphibious U.S. 93 93 ships 54 54 31 31 China 78 78 52 52 4 4 Russia 32 32 49 49 0 India 28 28 14 14 1 1 France 23 23 6 6 3 3 Britain 19 19 7 7 6 6 *Attack/guided missile submarines. | Source: International Institute for Strategic Studies

Expanding the fleet size could come at significant cost. The Congressional Budget Office estimated that building a fleet of around 350 ships could cost about 60 percent more per year than average historical shipbuilding budgets, with a completion date of 2046.

But a larger fleet could help reduce pressure on the Navy, according to Brian Slattery, a policy analyst at the Heritage Foundation, a conservative think tank. “They’ve had to push those deployments longer and longer because the Navy needs to be in all the same places in the world, and there are fewer ships to do it,” he said.

Others argue that the Navy’s resources are stretched because they have too many deployments and that a more modest strategy around the world would alleviate the strain. “To the extent that they are not in great shape, it’s because they have too many missions,” Mr. Friedman said.

4 Nuclear Weapons

After Mr. Trump tweeted his pledge to expand America’s nuclear capability, he told the talk-show host Mika Brzezinski of MSNBC: “Let it be an arms race. We will outmatch them at every pass and outlast them all.”

He has not specified whether he hopes to build more warheads or develop new weapons systems for delivering them.

The United States and Russia possess the vast majority of the world’s nuclear warheads, although both have reduced their arsenals under a series of treaties.

Estimated number of nuclear weapons 40,000 United States U.S.S.R./ Russia 30,000 20,000 10,000 Total for seven other countries ’50 ’60 ’70 ’80 ’90 ’00 ’10 40,000 U.S.S.R./ Russia U.S. 30,000 20,000 10,000 Total for seven other countries ’50 ’60 ’70 ’80 ’90 ’00 ’10 Source: Federation of American Scientists

Mr. Trump criticized the latest of those treaties, a 2010 agreement with Moscow called New Start, as “just another bad deal,” according to Reuters.

He has not clarified whether he will consider abrogating the treaty, which could open the way for the United States and Russia to expand their nuclear arsenals and capabilities.

Analysts say Mr. Trump’s call for a nuclear “arms race” could potentially cost billions. But as with other spending plans, he has not articulated a strategic goal.

While Mr. Trump has said that he wants to defeat the Islamic State, he has not explained how increasing the size of the military would accomplish that.

Mr. Trump’s focus on big-ticket items is mainly “useful in more conventional military campaigns,” said Michael C. Horowitz, a University of Pennsylvania professor who studies military leadership. “The kind of investments you would make if you were primarily focused on counterinsurgency campaigns are very different.”