(CNN) Defense Secretary James Mattis has written a letter of recommendation for former White House chief of staff Reince Priebus to join the Navy as a reserve officer, the Pentagon confirmed Friday.

The program is fairly common practice for the Navy, and has become known as a way for politicians to gain military experience.

"Secretary Mattis agreed to write a letter of recommendation on his behalf. The letter is consistent with applicable standards," said chief Pentagon spokesperson Dana White on Friday.

The process allows for career professionals to contribute their field's experience, but in the capacity of serving in the US military, and those accepted will generally go to Newport, Rhode Island, for two weeks of training.

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