The Mech 2300 is a Boss.
Taking down the Mech 2300 is a two stage process. First players have to damage its primary defense system sufficiently by using SA-16 which will cause Mech to power down briefly, leaving its power unit vulnerable, then use this window of opportunity to damage the power unit on top of the cockpit. Once mech is powered again, it will replenish all of its armor and the process will have to be repeated.
The Mech's protective glass is invulnerable to bullets, except in Easy difficulty where it takes only 20% damage from bullets. The power unit has a damage cap of 700 each time the Mech powers down.