Sen. John McCainJohn McCainKasich: 'I think political parties are on their way out' Five fights for Trump’s first year Trump wall faces skepticism on border 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.

"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.