The Mil Constructor is a machine that, as the name implies, creates Mils. They are found multiple times throughout the game and each with a varying amount of health before they explode. They only create Mil Grunt, and the Elite Guards. They only create Red, Green, and Blue grunts, however. Never a black or silver.
Typically these machines are destroyed with a coring charge or two, however others in the game are sometimes very tedious to destroy and often take up to five coring charges, their health changing with increased difficulty settings. There are two scenarios in the game where the constructor is invincible, one in "Do Ore Die", the constructor is required for the level to progress, and explodes after a scripted sequence in the level. and in the mission "Infiltrate the Compound", which is not needed for the player to progress, and only creates Mils when the Control Console is used.