The New York businessman said he wants to increase the Army to 540,000 troops, build out the Marine Corps to 36 battalions and add about 100 fighter craft to the Air Force, bringing the total to 1,200.
Mr. Trump also said he would build a “state of the art” missile-defense system and modernize naval cruisers to provide ballistic missile-defense capabilities.
The first-time political candidate didn’t put a price tag on his plan. Mackenzie Eaglen, a resident fellow at the conservative American Enterprise Institute, estimates that Mr. Trump’s plan could cost $55 billion to $60 billion more a year than the current budget caps for military spending.
The four-year cost of restoring the Army to 540,000 active-duty soldiers could be between $35 billion and $50 billion, she said. The cost over four years to expand the Navy’s fleet from 308 ships to 350 would be about $13 billion; the cost of building the Marine Corps to have 36 battalions would be about $15 billion over the next four years. Finally, building a 1,200-fighter Air Force could cost at least $25 billion, Ms. Eaglen estimated. The costs of Mr. Trump’s proposals, however, would cost more beyond the four-year estimates; building 42 ships, for example, would take years to complete and cost billions more.
“This is clearly ambitious and expensive,” she said in an email.
Anthony Cordesman, a defense and strategy expert at the Center for Strategic & International Studies, said Mr. Trump’s numbers were more a political statement to show his defense commitments to voters than a serious defense-policy proposal.
“Generic manpower or generic units or generic equipment has no military meaning,” said Mr. Cordesman.
Chris Harmer, a retired commander in the U.S. Navy and a defense-policy expert, said the broader point that the military is overtaxed and underfunded in its current missions abroad has merit. But he said that there was little need to increase defense if Mr. Trump is simultaneously proposing scaling back U.S. commitments.
“Mr. Trump seems to be advocating both a decrease in overseas commitments as well as an increase in military funding that doesn’t seem to make sense. He has talked repeatedly of decreasing U.S. commitment to our Asian allies, our allies in the Middle East and our NATO and European allies. If that is what he wants to do, there is no real reason to increase funding,” Mr. Harmer said.
Justin Johnson, a defense-budget expert with the conservative Heritage Foundation, said the U.S. military was in a “downward spiral” at the same time threats from Islamic State, Russia, North Korea and other international and nonstate actors were growing. Mr. Trump’s proposal to both spend more resources on defense while asking allies to contribute their fair share was a reasonable policy prescription, he said.
“The next president should do both things: rebuild the U.S. military and call for our allies to do more. I think that’s a reasonable step,” Mr. Johnson said.
Mr. Trump cited the Heritage Foundation’s work in his speech.
Before he could embark on a military buildup, Mr. Trump would have to convince Congress to rescind mandatory defense-spending limits, part of what is known as sequestration, or the sequester. Those limits were established as part of a 2011 budget agreement that set a decade’s worth of spending caps to try to reduce the federal budget deficit.
“As soon as I take office, I will ask Congress to fully eliminate the defense sequester and will submit a new budget to rebuild our military,” Mr. Trump said. “It is so depleted.”
Calls to end the sequestration cuts have increased as military officials have warned lawmakers that the reductions would jeopardize preparedness. But lawmakers have so far been only able to agree on temporary deals easing spending limits for both the military and domestic programs.
Many Republicans want to increase military spending, but Democrats for years have insisted that they won’t agree to any spending relief for the military unless domestic programs get an equal boost. While Republicans can push bills through the House with a majority vote, they need Democratic cooperation to get legislation through the Senate’s procedural hurdles.
“Our priority is spending for the military, so they’re trying to use this as a leverage point,” said Rep. Adam Kinzinger (R., Ill.), who supports boosting military spending. “We’re asking more and more of our military and yet giving them less and less resources over time.”
Democrats said Wednesday they aren’t willing to change their budget principles.
“We’ve long insisted that we restore funding for domestic spending on a one-to-one basis,” said Sen. Brian Schatz (D., Hawaii), a member of the Senate appropriations panel. “We’re not about to abandon it because Donald Trump is the new advocate for the old Republican position.”
Mr. Trump promised that the cost of his plan could be offset by, among other things, targeting tax cheats, eliminating waste in the federal government and reducing bureaucracy in the Pentagon.
In his speech, Mr. Trump also criticized Mrs. Clinton for her handling of Libya and the Middle East when she was secretary of state.
“Unlike my opponent, my foreign policy will emphasize diplomacy, not destruction,” Mr. Trump said, adding that Mrs. Clinton’s legacy is “only turmoil and suffering and death.”
“She’s trigger-happy and very unstable,” Mr. Trump said.
Mr. Trump said his administration’s foreign policy would be “tempered by realism” and would encourage “gradual reform” in the Middle East.
Brad Woodhouse, president of the pro-Clinton group Correct The Record, said Mr. Trump’s remarks show he “has no clue” about how to protect Americans. “Donald Trump has finally admitted that he has no strategy to defeat ISIS.”
The Clinton campaign has spent the week attacking Mr. Trump over military issues. In what was billed as a major national-security address in North Carolina on Tuesday, Democratic vice-presidential nominee Tim Kaine criticized the Republican nominee by name 61 times, calling him “unqualified and temperamentally unfit to serve as president.”
“Trump has offered empty promises and divisive rhetoric,” Mr. Kaine said. “Under his leadership, we would be unrecognizable to the rest of the world, and far less safe.”
A majority of voters don’t have confidence in either the Republican or Democratic presidential nominee to be an effective commander in chief of the nation’s military, according to an NBC News/SurveyMonkey online pollreleased Wednesday. But Mrs. Clinton had a wide lead—44% to 24%—when voters were asked which candidate they trusted to make the right decisions about using nuclear weapons.
—Byron Tau and Gordon Lubold contributed to this article.
Trump unveils plan to boost US military, Defeat the Islamic State