The Pentagon says President Donald Trump's former chief of staff is on track to join the Navy Reserve, buoyed by a recommendation from Defense Secretary Jim Mattis.

Reince Priebus, 46, served as chief of staff for about six months, beginning at the start of Trump's administration in January 2017. He also was chairman of the Republican National Committee from 2011 to 2017.

Pentagon spokeswoman Dana White says it is customary for Reserve applicants to request recommendations from members of Congress and other officials. She says Mattis agreed to write a letter for Priebus and it was consistent with applicable standards.

Trump's former press secretary Sean Spicer is also a reserve officer. He was often seen around the Pentagon doing his reserve duties during his White House stint.