Having only average speed and the second lowest armor and health, the Engineer is not well suited for gunning it out; however, he more than makes up for his shortcomings with his special ability to construct a sentry gun (SG), a stationary automated weapon that targets any enemy players it can detect, unleashing a hail of firepower at them. With a well-placed SG, an Engineer forms the backbone of a team's defense, able to defend two points at once. Once built, a so-called "level 1" SG consists of a turreted machine gun, which is somewhat slow to lock on to enemies, inflicts fairly light damage and is easy to destroy. It can be "upgraded" by any Engineer of the same team who hits it with his spanner (at the cost of 130 cells) to a level 2 SG. This replaces the single-barrel machine gun with an HWGuy-style minigun, making it very effective at cutting down lighter classes and increases its range and durability. The SG can be upgraded yet again to level 3, which adds a second minigun and a powerful rocket launcher to the mix, and another increase to range and durability. A level 3 SG can out slug even a heavily armored HWGuy under the right conditions.
As powerful as it is, the SG does have drawbacks. It only locks onto enemies that pass within its detection range, and it only sweeps an area of approximately 270 degrees, creating potential blind spots that can be exploited, especially if it is not well placed, or if the other team stays beyond its limited range. It cannot detect disguised Spies at all, who can safely bombard it with grenades. It rapidly consumes ammunition, requiring occasional trips to resupply areas, leaving it unguarded and vulnerable. Proper placement and maintenance of an SG is crucial to the Engineer's effectiveness.
In addition to the SG, this class can also construct:
- One-way teleporters: Ring shaped devices that teammates can use for quick jumps across larger maps. One teleporter the Engineer builds is designated as the "entry pad", and the second is its "exit pad". Opposing players cannot use them. They are fairly fragile and generate a distinct noise when activated, thus opposing teams are usually quick to find and destroy them.
- Ammunition dispensers: Stationary machines that slowly generate ammunition of all types, and can be used by any player — friend or foe. When a player touches an enemy dispenser, it sends an alert to its builder. For this reason, dispensers are sometimes more useful as a perimeter alarm at choke points (sometimes even temporarily slowing a player down). An Engineer can also detonate his dispenser at any time, causing incredible damage or death of the enemy player if the dispenser is fully loaded.
In order to construct the above items the Engineer requires cells converted from armor pickups or standard ammunition packs scattered around the map. The Engineer must make frequent trips to ammunition caches in order to upgrade sentry guns or re-stock ammunition dispensers. Teammates often support their Engineers by tossing unwanted ammunition to them whenever possible.
Aside from the SG, this class carries another of the most fearsome weapons in TFC — the EMP grenade. This potent weapon does not explode itself. Rather, it detonates the cell, rocket, and shell ammunition of any enemy within its area of effect (as well as any ammunition on the ground), approximately 15' radius, including through narrow walls and floors. This makes the EMP extremely deadly to classes that rely on cell ammunition, such as the Pyro and Demoman, but is also effective against Soldiers and HWGuys. The explosive damage caused by closely clustered foes is often enough to annihilate the entire group at once, even the lighter classes, who would otherwise not be particularly vulnerable to the EMP.
An Engineer can repair teammates' armor, or any other Engineer teammates' SGs, teleporters, or dispensers by hitting them with his spanner (at the cost of cells). This class spawns with up to 4 normal grenades, and is also armed with a double-barreled shotgun and a "railgun" (not to be mistaken for the Q3A weapon of the same name) that fires slow-moving green projectiles. While close to ineffective against normal opponents, this weapon has infinite range and is primarily intended for use against sentry guns.