Sen. John McCainJohn Sidney McCainHeatwaves don't lie: Telling the truth about climate change Overnight Energy: Lake Mead's decline points to scary water future in West | White House leads opposition to raising gas tax | Biden taps ex-New Mexico lawmaker for USDA post Lake Mead's decline points to scary water future in West 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.