I say Braddock's Expedition, a large column of British regulars 44th and 48th Foot with about 500 additional militia trying to capture the French fortress Duquesne led by Edward Braddock and his ADC George Washington were utterly destroyed in an encounter approx 300-900 French and Indians ( Moderate estimate is 400 ).
The British and French actually met each other and were equally surprised to met each other, but while the British went into panic the Indians effectively surrounded the column on the road with smart skirmishing while the French advanced in lines down the main road, the confused British who only knew how to stand in line started to fire on their American allies who were taking cover and were thus mistaken for enemies.
After some hours, General Braddock was killed and Washington managed to form a rear guard to protect the survivors.
British casualties out of 1300: 978 Casualties whereof 456 dead.
French & Allied casualties : 40 ( Most likely more )
