Retired Gen. James Mattis will emphasize his commitment to a military controlled by civilians in excerpts of the opening statement prepared for his confirmation hearing on Thursday morning.

Mattis said that civilian control of the military is a "fundamental tenet of the American military tradition," partly because those in uniform are often unable or unwilling to question or oppose the policy they're directed to implement.

"Both the commander-in-chief and the secretary of defense must impose an objective strategic calculus in the national security decision-making process and effectively direct its activities," Mattis said in the prepared remarks. "If the Senate consents and if the full Congress passes an exception to the seven-year requirement, I will provide strong civilian leadership of military plans and decisions."

Mattis will testify at a Senate Armed Services Committee hearing at 9:30 Thursday morning. Senators are also expected to vote on providing him an exception to the law requiring officers to be out of uniform for seven years before serving as defense secretary.

Mattis served in the Marine Corps for 44 years, most recently as the commander of U.S. Central Command. He retired in 2013 and was "enjoying a full life west of the Rockies" when President-elect Trump tapped him to be the Pentagon's top civilian.

The former four-star general said his priorities, if confirmed as defense secretary, will be "to strengthen military readiness, strengthen our alliances in league with our diplomatic partners, and bring business reforms to the Department of Defense by instilling budget discipline and holding our leaders accountable."

In what's expected to be a wide-ranging, cordial confirmation hearing, experts predict that Mattis will be questioned about his view of the path forward with respect to Iran, the fight against terrorists and some of the Pentagon's top acquisition programs that the president-elect has singled out, such as the F-35. Mattis is also likely to have to reconcile where his views differ from Trump's, including the use of torture. While Trump said he would bring back techniques like waterboarding, Mattis has said he does not need those types of interrogation techniques to collect intelligence.

Mattis is also certain to field questions on Russia, especially Trump's seemingly close relationship with Russian President Vladimir Putin, but did not mention the former Soviet Union in the prepared remarks.

Mattis was scheduled to speak at a House Armed Services Committee hearing on granting him a waiver to serve following his appearance at the Senate, but his testimony was cancelled after the transition team told him he couldn't go, according to multiple congressional aides. In response, some Democrats are saying they will not support the waiver.

The House committee will still meet Thursday afternoon to mark up its version of the waiver.

A panel of think tank and academic experts told senators this week that, while they would typically not support a waiver of the law requiring a seven year break after military service, they believe Mattis is worthy of an exception.