The Iroquois Mantlet is an Iroquois-specific siege infantry unit that has high hitpoints, a decent resistance to damage, and a moderate attack. Since the mantlet uses a ranged attack, it's appropiate to keep their distance. Due to their high health Iroquois mantlets are very good against defensive buildings, ranged units, and artillery.
With some boost from the WarChief, the Iroquois mantlet can have hitpoints that exceeds over 1000 with all upgrades. This allows them to be very effective when deployed in numbers as cannon fodder for protecting units that are weak to range. With the Siege Discipline shipment their population cost is dropped to only 1 which makes mass production of this unit very easy.