Here is a link in support of my consideration of Assaye, India 1803.
It can be noted that, as the link quotes, Wellington considered it his hardest battle, and did not care to speak of it, but when asked , wuold repliy with one word grunted - 'Assaye'.
Although outnumbered ten to one, General Arthur Wellesley defeated the well trained Mahratta army in one of the fiercest battles in India. It was the first of many victories by the future Duke of Wellington, and the bloodiest for the number, he recalled, that I ever saw.
http://www.britishbattles.com/second-mahratta/assaye.htm
The '74th Highlanders' quoted became 2nd Bn. The Highland Light Infantry, and, as the link states, they lost all their Officers that day,but one wounded left on the field; they also lost all their NCO's but the quarter-master, down to the Corporals, who continued leading their remnants in the battle.The were awarded the honour of an Elephant on their badge, and each year the Regiment celebrates the battle by allowing the Corporals to take over command of the Regiment for the day. Assaye Day.
Uniquely, I believe, The Highland Light Infantry are in fact not Light Infantry; they have a Support Company, and march at the normal infantry 120 paces as opposed to 180. The 'Light Infantry' title is another hard earned battle honour.