|Technician: Engineer||Tier 3|
|Basic (3 pt): You can now select a less noisy version of the sentry guns, making them much less likely to be targeted by enemies.|
|Ace (6 pt): You can now toggle AP rounds on your sentry guns, lowering the rate of fire by 75%, but increasing the damage by 250% and allowing it to pierce through enemies and shields.|
Engineering Basic does pretty much what it says on the tin, in that it unlocks the second, suppressed version of the Sentry Gun that has a lower chance to be targeted. Note that the Silenced Sentry Gun is technically a completely different deployable (although it gets all the same benefits from skills as standard Sentry Guns) and must be chosen in the inventory in order to be used.
While the Suppressed Sentry Gun is technically equipped with a suppressor, note that it does not behave as a player's silenced weapons would - Suppressed Sentry Guns are not effected by suppressor-related effects of The Professional skill, and will alert guards and civilians in a large radius if it happens to spot and shoot a guard while in stealth.
Acing the skill grants all your Sentry Guns - both suppressed and standard - the ability to fire armor piercing ammo instead of their normal rounds. These bullets will punch through shields (except for those of Captain Winters and his brigade), the body armor of Maximum Force Responders ("Tans"/"Browns"), and thin walls. Sentry Guns will still have non-AP ammo loaded by default when placed, but facing your turret and pressing the interact key will swap between AP and non-AP rounds. Note that this will not be prioritized over other interactions, such as picking a lock, holding a bag which can be thrown, or picking up the sentry gun itself.
While set to AP rounds, the Sentry Gun fires at only a fourth of its normal rate, but each shot does 250% more damage, resulting in the AP firing mode having a DPS equal to 7/8 that of the non-AP rounds on average, not counting damage blocked by Shields. However, each AP round fired by a Sentry Gun takes just as much ammo as a non-AP round, so the ammo reserves of an AP sentry will last four times as long as a default sentry's.
While the Suppressed Sentry Gun is not really that spectacular, strategically-placed ones can still be useful when trying to thin out an enemy mob, with their lowered aggro rating making enemies less likely to target them during combat. This could be used to position them in more risky, but more useful, places, such as next to an enemy spawn point where cops must climb over a fence or rappel from a roof before being able to retaliate. Emphasis is still on less, however, as they will still be shot at if there are no players around or if they are closer to the enemy than the players themselves.
With Engineering Aced, toggling AP mode on suppressed sentries can provide the crew with "stealthy" Shield busters, allowing them to circumvent their greatest weakness at the cost of a significantly lowered fire rate.
AP sentries are ideal for situations in which the sentry will be far from the action, such as thinning out the herd at spawn points while the players work on a distant objective. Their ability to take down Shields makes them completely self-reliant against all enemy types but Captain Winters, and the greater ammo efficiency afforded by AP rounds will let them stay in the fight much longer before needing a reload.
- Even though the Sentry Gun only ever fires AP rounds when told to do so while Engineering is aced, all Sentry Guns have AP rounds attached on the model upon deployment, even without owning this skill.
- Considering the fact that the Kobus 90 (or its real-world equivalent, the FN P90) which has been built into the Sentry Gun can not normally fire armor-piercing ammunition, numerous modifications must have been made to the weapon in order to allow it to not only fire AP rounds, but swap between AP and non-AP rounds without missing a beat.