In every campaign, most levels involve the Survivors attempting to reach a safe zone and close the door once they are all safely inside. However, the final level in each campaign requires the Survivors to call for rescue and either survive a prolonged onslaught until rescue arrives, pass through an especially challenging gauntlet of Infected to reach an escape vehicle, or (in Dead Center and The Passing) collect and utilize fuel cans to enable their escape.Each Survivor can carry one each of five categories of equipment: primary weapons, secondary weapons, throwable weapons, major medical supplies (which also includes ammunition upgrades) and minor medical supplies. Primary weapons are broken down into four tiers based on their availability and attributes.