"Johnny I Hardly Knew Ye" (AKA Johnny We Hardly Knew Ye, and Johnny I Hardly Knew Ya) is a popular Irish traditional anti-war and anti-recruiting song. It is generally dated to the early 19th century, when Irish troops served the British East India company. The original refers to the soldiers from Athy, County Kildare that fought in "Sulloon" (Ceylon-nowSri Lanka) for the East India Company (in what history knows as the Kandyan Wars though the term was not familiar to the Irish). It has become a definitive anti-war song.
You can hear here the version by The Dannan and Mary black