The U.S. Senate on Tuesday confirmed Army Secretary Mark Esper to be secretary of defense, ending the longest period by far that the Pentagon has been without a permanent top official.

The Senate backed Esper, a former soldier and lobbyist for weapons maker Raytheon Co., to be President Donald Trump's second confirmed leader of the Pentagon by 90-8.

Esper, 55, received strong bipartisan support despite some sharp questioning during his confirmation hearing by Democratic Senator Elizabeth Warren about his ties to Raytheon and his refusal to extend an ethics commitment he signed in 2017 to avoid decisions involving the company.

Warren, a 2020 presidential hopeful, was the only member of the Senate Armed Services Committee to voice opposition to Esper's confirmation during the hearing.

Raytheon is the third-largest U.S. defense contractor.

Esper's past as a Raytheon lobbyist drew criticism over a conflict of interest as Raytheon produces the U.S.' Patriot missile defense system, the rival of Russian S-400 systems and a thorny subject that has caused diplomatic rift between Ankara and Washington.

Ankara signed a contract in 2017 to purchase the S-400s from Russia, after efforts to purchase the Patriot defense system from the U.S. failed.

The U.S. halted in June training for Turkish pilots as a step in winding down Turkey's participation in the F-35 program, in retaliation to the deal.

Critics argued that that his position as a negotiator in the S-400 talks would be tarnished as he had worked for seven years at Raytheon before he joined the Pentagon in 2017. Many also underlined that Esper's position might have negative implications for the company.

More over, Esper also has a two-year recusal agreement, which obligates him to recuse himself from all matters that involve Raytheon while he is employed at the Pentagon. The agreement naturally includes the Patriot system as it is produced by the company.

There had been no confirmed defense secretary since Jim Mattis resigned in December over policy differences with Trump. Many members of Congress from both parties had urged the Republican president to act urgently to fill the powerful position.

Senate Majority Leader Mitch McConnell called on members to support Esper as he opened the Senate on Tuesday morning.

"The nominee is beyond qualified. His record of public service is beyond impressive. His commitment to serving our service members is beyond obvious. And the need for a Senate-confirmed secretary of defense is beyond urgent," McConnell said.

An army veteran, Esper had served as a congressional aide and a Pentagon official under Republican President George W. Bush before working for Raytheon. He has been army secretary since November 2017.

Trump's previous pick to be secretary of defense, former Boeing Co. executive Patrick Shanahan, withdrew from consideration on June 18 after reports emerged of domestic violence in his family.

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