Throughout 1903, the Senate minority was blocking several nominations put forth by the White House. President Roosevelt should have been able to wait for that Congressional session to adjourn and make his recess appointments before the next session was scheduled to begin, by Constitutional mandate, on December 7 of that year. However, House Speaker Joe Cannon refused to go along, keeping the House in session throughout the break.
In response, the Senate leadership concocted a plan. On the big day of December 7, the Senate convened, adjourned, and immediately began an entirely new session. As The New York Times report had it the next day:The conclusion has been reached that between the time of the falling of President pro tempore Frye’s gavel signifying the conclusion of the extraordinary session and the calling to order of the Senate in the regular session of Congress, an appreciable lapse of time occurred. In this time the appointments technically were made. … There was but one fall of the gavel, but one stroke, and but one sound.And in that instant, Roosevelt made 168 military promotions that normally would have to have been approved by the Senate, as well as “about 25 civilian appointees.”
Was it legal? No one knows with certainty, as it wasn’t adjudicated in the courts.