While the NFL does recognize the records of the American Football League (1960-1969), it does not include AAFC marks in its record keeping.
No one team ever seriously challenged the Browns but the San Francisco 49ers, also destined to wind up in the NFL, came the closest. They defeated the Browns in 1946 and again in 1949 and came close twice in the flawless 1948 season.
Both teams were 10-0 when they met in Cleveland before 82,769, the largest crowd in pro football history up to that time. Cleveland won 14-7 and had an even closer call two weeks later in San Francisco in a 31-28 squeaker.
The Chicago Bears sailed through the 1942 NFL schedule undefeated and untied. The reigning NFL champs, the Bears, were favorites to win their third consecutive title when they met the Washington Redskins in the 1942 Championship game. However, the Redskins defense was up to the task and surprised the Bears 14-6. The Redskin victory had an extra measure of satisfaction, since it was the same Bears team that two years earlier humiliated Washington 73-0 in the 1940 title game.
Having an undefeated and untied regular season, only to lose in the championship game, was not a new experience for the Bears. In 1934, the New York Giants upset the 13-0 Bears were upset 30-13 in the championship game.'34 and '42 Bears go undefeated