"Siege Workshop units are faster."—In-game description
Siege Drill is a Big Button technology in Age of Empires III: The WarChiefs that is unique to the Iroquois and can be researched at the Siege Workshop. Once researched, it increases the speed of Rams, Mantlets, and Light Cannons by 10%.
Siege Drill is of a vital importance to keep an Iroquois army moving quickly.