The Pentagon's top leaders defended the Trump administration's new strategy for Afghanistan in detail Tuesday, saying it will last as long as is needed and includes provisions under which U.S. troops will be placed alongside Afghan troops at lower levels of command to provide them with better coalition air support.

Defense Secretary Jim Mattis and Marine Gen. Joseph Dunford Jr., the chairman of the Joint Chiefs of Staff, described the strategy in separate hearings before the Senate and House armed services committee as an effort to win, rather than not lose, a conflict that began 16 years ago. They faced skeptical lawmakers, including committee chairman John McCain, R-Ariz., who lambasted a lack of transparency by the administration about its plans.

"In the six weeks since the president made his announcement, this committee and the Congress, more broadly, still does not know many of the crucial details of this strategy," McCain said. "This is totally unacceptable. I repeat: This is totally unacceptable."

The hearings mark the first time that Mattis and Dunford have elaborated in great detail on what they call President Donald Trump's "South Asia Strategy." Trump announced Aug. 21 that he would continue U.S. involvement in the war in Afghanistan and send a few thousand more troops, even though his initial instinct told him not to do so.

Citing a desire to keep enemy forces off-balance, the Trump administration has declined to disclose some commonly released details about the plan, including exactly how many additional troops will deploy. Mattis has said about 3,000 U.S. troops will join 11,000 American forces and 6,800 additional international troops from allied nations. McCain and defense officials, speaking on condition of anonymity in order to describe Pentagon deliberations, put the number of additional U.S. troops at closer to 3,500.

Mattis, a retired Marine general who once commanded troops in Afghanistan, said Afghan commandos who have fought with U.S. military advisers alongside them "have won every time they have fought the enemy," and that those who have fought alone "have not won." The Pentagon is adding more Special Operations troops for that purpose, Mattis said, as well as more U.S. advisers so that when a conventional Afghan unit carries out offensive operations, they will have them.

Some of the additional U.S. military advisers will be assigned to work with an Afghan corps, a large unit that includes thousands of soldiers. Within that corps, there will be a brigade of a few thousand Afghan soldiers working closely with American advisers, enabling a kandak — a unit of a several hundred Afghan soldiers - to better carry out offensive operations, Mattis said.

"They have not had them in the last several years, and that means they were not able to get swift access to NATO air support and fire support," he added.

McCain, who often criticized the administration of former president Barack Obama for its decisions on Afghanistan, said that he admires Mattis and Dunford, but that he thinks the amount of information they have shared about their plans is severely lacking. Ending the Obama administration's "foolish policy of arbitrary timetables for withdrawal" and shifting to a conditions-based approach in Afghanistan was encouraging, McCain said, but more information is needed.

Mattis introduced a new acronym to explain the Trump administration's plan: R4+S. It stands for regionalizing the approach to consider involvement by India, Pakistan, Iran, Russia and China, realigning the military effort to put more U.S. advisers at the brigade and battalion levels of Afghan units, reinforcing the effort with additional U.S. troops, looking for ways to reconcile with "fence-sitters" in Afghanistan who might work with the government, and making sure that the 320,000 Afghan forces are sustained as they face a tough fight.

The Trump administration has stressed that pressing the Pakistani government about its relationships with extremist organizations in Afghanistan will be part of the equation. Mattis and Dunford said that broadly, that will require the United States to build more support internationally to sway Pakistan from doing so. More specifically, Mattis plans to visit Islamabad soon, he said.

Mattis said there are several signs that the situation on the ground in Afghanistan is changing. He cited a recent decline in the Afghan military's fatalities and a boost in U.S. airstrikes as examples, without providing specific statistics. The number of airstrikes, Mattis said, are higher than at any point since 2012, as the Obama administration's surge in troops there came to a close.

"That's a tactical effect that will make the Afghan army bolder, and it will give them more opportunities militarily to take the fight to the enemy," Mattis said. "And that would be the way, as we take the fight to the enemy, we convince the Taliban, 'You're not going to win this by killing.'"

Dunford, who was the top general in Afghanistan under Obama from February 2013 to August 2014, said the decision to reduce military advising to conventional Afghan forces, along with aviation, artillery and intelligence support beginning in January 2015 left the Afghan military without the support they needed on the battlefield.

"My military assessment is that we drew down our advisory effort and combat support for the Afghan forces too far and too fast," Dunford said. "As a result, the Taliban expanded territorial and population control and inflicted significant casualties on the Afghan army and police, while the campaign lost momentum."