Outpost is a PvE mode featured in Insurgency and Insurgency: Sandstorm.
Insurgency (2014)
"Hold your ground for as long as possible"
— In-game description
Outpost is a coop gamemode in Insurgency, where you must defend the cache from AI enemies that also increase in number as you progress farther into the waves.
Every round, the health of the cache resets.[1]
Maps
Insurgency: Sandstorm
Overview
In Outpost, the Security team is tasked with holding an objective against 7 waves of enemies. As waves progress, the Security team gets more credits to spend on weapons and equipment while the AI Insurgents gain increased firepower, more enemy varieties, and numbers. Every objective lost sets the team back to a fallback point until they either clear all 7 waves or lose all points.
Strategy
Organize! - Having an organized team can help watch angles and cover each other's backs. Communication helps a lot, so try to point out places where the enemy is attacking from and coordinate properly!
Understand the maps - Some maps have very obvious lanes in which the bots follow and can be easily locked down by a competent Gunner or an artillery strike. Understanding where these are can be crucial in stopping the enemies' advance before they come into the objective.
Have a command unit - Having a commander and an observer chaining artillery strikes or calling in helicopters helps put pressure off of the team stuck defending. Especially in the later rounds where "hordes" of enemies start running down the objective, a well timed A-10 strafe or helicopter support helps thin their numbers.
Use your equipment - When entering the objective, the enemy bots usually pile up around doorways and entrances. Use this knowledge to your advantage and throw incendiary/ molotovs to block entrances or toss frags to clear the point.
Use their equipment against them - In later rounds, the bots start getting up armed to machine guns and rocket launchers, and when they die they'll drop it onto the ground. Picking up an MG3 or an RPG-7 is quite the asset to have, allowing you to rack up more kills easier!