Sen. John McCainJohn Sidney McCainRubio asks Army to kick out West Point grad with pro-communist posts The VA's woes cannot be pinned on any singular administration Overnight Defense: Mattis offers support for Iran deal | McCain blocks nominees over Afghanistan strategy | Trump, Tillerson spilt raises new questions about N. Korea policy MORE (R-Ariz.) performed the formal ceremony of pinning the new insignia on Brown, according to the Sun Chronicle of Attleboro, Mass.

Brown had previously served as a lieutenant colonel.

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"I never thought I would be colonel," Brown said according to the paper.

Brown called McCain, who has been a mentor to him in the Senate, a national hero.

The junior senator from Massachusetts has served in the National Guard for 32 years.

Throughout the day a number of Brown's Republican colleagues in the Senate congratulated his promotion.