They opened the decade with three championships in four years. The Bears were the toughest on the field and the smartest in the coaching department. In fact, it was their introduction of the modern T that made the most profound change on the game.
Chicago was the only team that had the T formation with a man in motion. Halas had fooled around with the ancient tight T of the 1890s, but in 1930 he hired Ralph Jones, the athletic director at nearby Lake Forest Academy, to spiff it up. Jones widened the linemen's splits, spread one receiver and sent a back in motion, usually Grange, the left half. He had a feel for this kind of trickery and would occasionally pivot and motion back the other way. It was innovative but not particularly devastating, used to mix up the game plan, sharing time with the conventional single wing.
Enter Clark Shaughnessy, "one of the great innovative minds," according to Bill Walsh. Shaughnessy, coaching a dying program at the University of Chicago, doubled as a consultant for the Bears. He fine-tuned the T, and the formation became the Bears' basic offense in 1940. That year, after Chicago walloped the Redskins 73-0 in the NFL title game, and Stanford, coached by Shaughnessy, capped an unbeaten season with a Rose Bowl victory, the T became the new darling of the football world.
Chicago players and coaches spread the word about the T. Halas and Shaughnessy gave coaching clinics. Hall of Fame quarterback Sid Luckman returned to his alma mater, Columbia, to help install the system. By 1944 more than half the college and professional teams were using it. National champions Notre Dame and Army called on Luckman to teach it to their quarterbacks, and during the Army-Notre Dame game of '47, Luckman, whose Bears would play the Packers the next day, was in the Irish press box in South Bend helping with the play-calling. By 1949 only a handful of college programs and one NFL team, the Steelers, clung to the single wing.
The modern T is still in place, with modifications, of course, and at 60 it remains the longest-running formation in the history of the game.