The Sentinel is an unlockable light sniper class focused primarily on base defense and attacking. With some of the longest ranged weapons in the game, the Sentinel can become quite a nuisance to light base defenses and flag runners.
 Primary Weapon
 Secondary Weapon
 Belt Item
|Class Cost Table|
|Item||Gold Cost||XP Cost||Mastering Cost||Total XP|
|Sentinel MK I||Free||Free||15000||15000|
|Nova Blaster MX||160||18000||15000||33000|
|Focused Claymore Mine||160||18000||15000||33000|
 Class Roles and Tips
For the sentinel, good positioning (at competitive level) comes down to roughly three things:
1. Spotting enemy routes.
2. Lining up enemy cappers.
3. Avoiding enemy offense.
On nr. 1: Other than killing cappers in the field or hindering their chance to regenerate health during routes, the sentinel usually plays another important role on the team: the spotter. Essentially, the spotter's job is to find all incoming cappers before they reach the flag and determine which direction they will attempt to enter the base. This is done to improve the chances of the defense stopping the cappers. Knowing where and when to look makes defending the flag much easier, especially for the Heavy on Flag.
Good spotting positions must thus be able to see all or most cap-routes at all times. The longer time the cappers spend in vision of the sentinel, the better the position. The position is even better if key routes require the capper to stay in certain points of the sentinel's field of view for a long time; for instance, if he is moving towards the sentinel at one point he will be "moving less" from your perspective than if he was moving orthogonally (at a 90 degree angle) from your position. Additionally, many flag runners will take return routes that require large jumps. In these situations, the capper's speed will reach zero at the apex of their jump, giving the sentinel a small window of opportunity to get an easy shot in.
All these points of slow movement make for great positions to continually press the "spot" button (Default: Left Alt), so if a position has many or key routes that have to go through these spot-points, it is a good position for the sentinel. Players learning how to use the sentinel should strive to learn how long cappers spend in the spotting positions, and never fail to check that area before that amount of time has passed. Players may find it beneficial to play pathfinder themselves to learn how they think and which routes are commonly used.
On nr 2: As covered under the Aiming section, lining up targets is important for consistent aim. This should be weighed against the spotting capabilities of the sentinel, and generally be considered of lower value, as you are often improving the efficiency of your teammates by spotting, but only improving the efficiency of yourself by getting good aiming positions.
On nr 3: There is a reason sentinels are almost never found on the flag stand in competitive matches: it takes just one spinfusor hit to kill them. Thus sentinels are found in obscure locations, generally of a high altitude to discourage the offense from killing them. Spawn towers and cliffs with view of half the map are frequently used, as it not only takes a lot of time and jetpack energy to reach these points, but also warns the sentinel of the incoming hostiles by the sound of their jetpack and drains energy that could be used by raiders as shields. Thankfully altitude also improves the spotting capabilities of the sentinel, so it is to be treasured indeed from to positional perspective. Standing on the very top of a peak or tower, while improving overall vision, can however restrict the movement of the sentinel and make it difficult to dodge spinfusor shots, therefore it is advised to give up even a good amount of height in trade off for mobility, coupled with your offence calling out where the enemy offence is located, before they are given chance to fire at you.
Aiming can be divided into three tactics:
2. Prediction and Timing.
3. Flick shotting
Tracking is a method used generally with hitscan weapons: Using the mouse to follow the movements of the target and keep the center of the reticule directly on the target while shooting it periodically. At long ranges this can be an extremely difficult feat to pull off, as the targets are very small, and often fast moving, but it is the preferred tactic of many. When the target is on the ground, tracking and flick shotting is usually the preferred method, because it takes into account the erratic movements and direction switches that is possible when a player is on the ground; however at long distances or high speeds, it can prove to be a very difficult task to accomplish.
Predicting and timing is then used when the target is moving in predictable patterns, allowing for easy hits. This is useful for hitting incoming cappers in particular, as one can usually quite easily distinguish the trajectory of a capper on his route. This tactic is a two step process: First, the player predicts a location the target will be shortly and places their crosshair there. Second, they pull the trigger once the target lines up with the crosshair. This tactic requires supreme reflexes, as many times the difference between a hit and a miss is less than half a second.
Flick shotting is, in summary, moving the crosshair over a target and pulling the trigger the moment it lines up with the target. This is particularly useful when the target is somewhat close, or is very erratic, such as when he is on the ground and is aware that he is being sniped. As the flick is completed so swiftly, movements to dodge are close to impossible aside from blind strafing.
Sniping in general is best done in places where opponents line up with the sentinel's position, that is to say when he is flying away or towards the player. This is because he seems to be moving less in the sentinel's field of view, and a slower target is much easier to hit. However, a capper will not always be flying directly to or from the player's position, but one can make up for this by waiting for certain points in the parabolic movements of targets.
In all cases, the best method is executed prior to lining up a shot and comprises proper positioning. A sentinel lined up with a fleeing or approaching flag runner is almost assured to hit, while one perpendicular to it is subject to the following rough calculation. Assuming a flag runner travels at 250 kmph (which unfortunately isn't even the velocity threshold of the game) and assuming the width of the torso to be about .3 meters, the window of opportunity to hit a flag runner at those velocities at any range is a whopping 1/227 of a second (or about 0.004 seconds). For reference, United States Air Force testing has found 1/220 seconds to be about the maximum threshold at which trained pilots are able to identify a flashed silhouette, making this sort of timing on the very edge of human perception, much less ability to react and execute. Unfortunately, even if one had the training to do so, it is unlikely that an individual's hardware is running at sufficient framerates to even render the actual position of said flag runners. In other words, Sentinel's at right angles to fast moving targets should employ the Spray-N-Pray methodology while moving to a better location and hammering on the following voice game commands - "VGS", "VAB", "VAC", "VAF", "VFR", and possibly "VGCG"
The mark of the good sentinel is not only in his aim but also in his understanding of his equipment. One must learn the difference between the four sniper rifles available, and what situations they excel best in. These are all covered in their respective articles, along with perk use.
Choosing the grenades versus the Claymore Mines should also be taken into account, especially when dealing with individuals who devote themselves to distracting and/or killing sentinels. Grenades are more versatile, but claymore mines can alert the sentinel to furtive infiltrators attempting to make surprise attack. Even some of the best players do not expect a reverse surprise attack from grenades, however.
 Video guides
Roxton's Sentinel Guide: https://www.youtube.com/watch?v=J18FuvSYw8I
Primary weapons guide(thanks to Yamiks): http://www.youtube.com/watch?v=4Z00BYoJWO4