Sentries are floating balloons with underslung turrets that can rotate in 360 degrees as well as pitch their gun up and down to lock onto the player and unleash a shedload of bullets.
Whether they drop from airships or emerge from entrances in the level, Sentries will spread out through the level hunting you and raining fire down from above if you're unlucky enough to run in front of their scope.
Let's take a look at how the Sentry went from initial sketches to what's in game:
|First pass colour|
|Recolour to give good squad balance|
|Modelled, turret reworked to accomodate SMG design|
|Adding in materials|
|Final Model In Engine|