Operation Market Garden. The largest airborne operation of all time. Also, a miserable failure.
For those who don't know, the operation plan's strategic context required the seizure of bridges across the Maas (Meuse River) and two arms of the Rhine in Netherlands in World War 2. This was supposed to be achieved by the surprise dropping of around 40,000 airborne troops deep into Nazi-occupied Netherlands in September 1944, and the rapid advance of an entire armored division, brigade and 2 infantry divisions through these bridges. What could have been the most successful allied operation during the WW2 soon turned into mayhem when the paratroopers were overrun and the bridges re-occupied by the Germans, and also because the armored drive encountered a lot more resistance than expected. The operation had to be ditched and the survivors evacuated.
The phrase "A bridge too far" comes from a comment made by British Lt. Gen. Frederick Browning, deputy commander of the First Allied Airborne Army, who told Field Marshal Bernard Montgomery before the operation, "I think we may be going a bridge too far." It has come to signify any "act of overreaching".