Donald Trump laid out plans on Wednesday to jettison current defense-spending caps and embark on a military buildup that includes big outlays for ships, planes and troops.
The Republican presidential nominee also said that, if elected, he would give the Pentagon 30 days to present a plan for destroying Islamic State.
Mr. Trump used the speech here to counter attacks from Democratic rival Hillary Clinton, who has repeatedly criticized Mr. Trump’s military and foreign polices this week. The former secretary of state has asserted that the New York businessman’s “whole campaign has been one long insult” to those in military service. Mr. Trump called Mrs. Clinton “trigger happy” in response.
The candidates were set to offer their dueling visions of national security on Wednesday night in back-to-back appearances during a forum televised on NBC. Mrs. Clinton took the stage first, after Mr. Trump won a coin toss and elected to appear in the final segment.
She said the most important quality the next commander in chief must possess is “an absolute rock steadiness mixed with strength to be able to make the hard decisions.” She added that “I’ve had the unique experience of watching and working with several presidents, and these are not easy decisions.”
Mrs. Clinton was also asked pointed questions about her use of a private email during her tenure as secretary of state, which she said was “a mistake” that she wouldn’t repeat.
The discussion came as voters rank national security higher as a priority than in any other presidential election in the past generation, and neither candidate has gained a decisive edge on the issue.
A majority of voters said they weren’t confident in either nominee’s ability to be an effective commander in chief, according to an NBC News/SurveyMonkey online poll released 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.
In his speech, Mr. Trump said, “Today, I’m here to talk to you about three crucial words that should be at the center, always, of our foreign policy—peace through strength.”
Mr. Trump said he wants to increase the number of active Army troops to 540,000 from 490,000, and boost the number of Marine Corps battalions to 36 from 23, or an extra 12,480 troops. He promised to build a Navy of 350 surface ships and submarines, up from 275 ships now, and to add about 100 fighter craft to the Air Force, bringing the total to 1,200.
Mr. Trump didn’t put a price tag on his plan. Mackenzie Eaglen, a resident fellow at the conservative American Enterprise Institute, estimated that Mr. Trump’s plan could cost $55 billion to $60 billion more a year than the current military budget.
Her estimates include some of Mr. Trump’s proposals. For example, the four-year cost of boosting the size of 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 to 350 ships would be about $13 billion; the cost of increasing the size of the Marines to 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 would climb far above the four-year estimates, according to Ms. Eaglen. Building 42 ships, for example, would take years to complete and cost billions more. “This is clearly ambitious and expensive,” Ms. Eaglen said in an email.
Anthony Cordesman, a defense and strategy expert at the Center for Strategic and International Studies, said that 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 was overtaxed and underfunded in its current missions abroad has merit. But he said that there was little need to increase defense spending if Mr. Trump is simultaneously proposing scaling back U.S. commitments in Asia and the North Atlantic Treaty Organization.
“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 the 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, which Mr. Trump cited in his speech, said the U.S. military was in a “downward spiral” at the same time that threats from Islamic State, Russia, North Korea and others were growing.
“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.
Before he could embark on a military buildup, Mr. Trump would have to persuade 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.
Calls to end the sequester have increased as military officials have warned lawmakers that the cuts jeopardize preparedness. But lawmakers have 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 say they won’t agree to any spending increases 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.). “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 said that the cost of his plan could be offset by, among other things, targeting tax cheats, eliminating waste in the federal government and reducing Pentagon bureaucracy.
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.
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.”
Mrs. Clinton has proposed ending the defense sequester cuts, but only if they are paired with an increase in nondefense spending. Her defense policy also emphasizes innovation aimed at countering emerging threats such as cybersecurity and terrorism. Like Mr. Trump, she has promised to curb waste and inefficiencies in the military.
She and Mr. Trump differ primarily on the role of U.S. allies. Mrs. Clinton has defended robust U.S. alliances as a key pillar of U.S. national security. Mr. Trump has been more skeptical of a U.S.-led global order and has been critical of interventions or proposed interventions in countries such as Libya and Syria.
“Our armed forces fight terrorists together; our diplomats work side by side. Allies provide staging areas for our military, so we can respond quickly to events on the other side of the world. And they share intelligence that helps us identify and defuse potential threats,” Mrs. Clinton said in a July speech on national security and defense.
The Clinton campaign has spent this week attacking Mr. Trump over military issues. In a national-security address in North Carolina on Tuesday, Democratic vice-presidential nominee Tim Kaine criticized called Mr. Trump “unqualified and temperamentally unfit to serve as president.” He added, “Under his leadership, we would be unrecognizable to the rest of the world, and far less safe.”
—Byron Tau and Gordon Lubold contributed to this article.
