WASHINGTON -- The $30 billion in requested additional defense funding for fiscal year 2017 would be used to strengthen the military and protect the nation against emerging global security challenges, Defense Secretary Jim Mattis said on Capitol Hill Wednesday.

At a hearing of the Senate Appropriations Subcommittee on Defense, Mattis warned that hesitation in investing in defense would deepen the "strategic mismatch between our future security and the military means to protect our people and freedoms."

The secretary appeared at the defense budget and readiness hearing with Marine Corps Gen. Joe Dunford, the chairman of the Joint Chiefs of Staff.

"The security situation facing our country has become more challenging," Mattis said. "The looming threats have outstripped the level of resources we have been allocating to defense."

GOOD STEWARDS OF TAXPAYER'S MONEY

President Donald J. Trump's request for the additional $30 billion represents the first step in a three-part, multi-year effort to restore readiness, Mattis explained.

This year's budget appropriation, including the requested additional $30 billion, is needed to "get our aircraft back in the air, our ships back to sea, and our troops back in the field with refurbished or new equipment and proper training," the defense secretary said.

"We base this request on a realistic appreciation of the capacity we need to fight and win on the battlefield," he said, noting the next phases of the effort focus on fiscal year 2018 and several years beyond.

The department is aware of the sacrifices of the American taxpayers in making the additional funding for fiscal year 2017 possible, Mattis said. The department takes the responsibility of being wise stewards seriously."

The $30 billion in additional funds includes a base budget request of $24.9 billion and an overseas contingency operations budget request of $5.1 billion.

The additional $30 billion funding request brings to $619.2 billion the amount requested by the Defense Department for fiscal year 2017, according to the DOD comptroller's office.

HIGHLIGHTING MILITARY SUPPORT OF DIPLOMACY

Mattis highlighted the importance of military support of diplomatic efforts, saying diplomatic solutions are the preferred options.

"Our military must ensure that the president and our diplomats always negotiate from a position of strength," he said. "Global threats require a global response, applying the full weight of our own and our allies' power, allies which are also increasing their defense outlays."

Military deterrence, the defense secretary said, is only credible if military strength is sufficiently formidable that allies can confidently align with the United States in tempering adversaries' designs.

GLOBAL CHALLENGES THREATEN NATIONAL SECURITY INTERESTS

The global security challenges threatening national security interests are numerous, Mattis told the senators.

"We see Russia and China seeking veto power over the economic, diplomatic and security decisions of nations on their periphery," he said. "Terrorist groups murder the innocent and threaten peace in many regions and target us."

In addition, the secretary noted North Korea's "reckless rhetoric and provocative actions" with its nuclear activities.

"This situation calls for our department to maintain a safe and secure nuclear deterrent and a decisive conventional force that can also fight irregular enemies since our military must be able to counter all threats facing us," Mattis said.

FUNDING REQUIRES 'HARD CHOICES' WITH 'SUSTAINED COMMITMENT'

The defense secretary acknowledged "hard choices" will have to be made in funding the department.

"With the help of the Congress, I believe we can build a force that is more lethal, without placing an undue burden on the American economy," he said.

But, in order to do so, DOD needs a "sustained commitment from Congress in the form of additional funding and regular on-time budgets," Mattis said.

(Follow Lisa Ferdinando on Twitter: @FerdinandoDoD)