Harry Potter-What year were the Marauders in during The Prank that almost killed Snape?

Remus mentions that James went after him "at great personal risk" but I don't remember if a specific year is given or not. It seems like because James was risking his life, it happened between second year (when they found out Remus was a werewolf, or possibly end of first year) and fourth year, aka, before they became Animagi, but Snape tells Dumbledore Sirius was "capable of murder at the age of sixteen". So, then, when did it happen?