The Tal'darim stole a number of sentries from the Daelaam and reprogrammed them violently, replacing their shield generators with on-board targeting systems. However, their force field generators remained intact. The Daelaam came into usage of the havocs during the End War.
The havoc lacks an innate attack like the sentry and energizer, being a purely supportive unit. It is able to use Force Field, and has the passive ability "Squad Sight," which boosts the range of units in a radius of 4 from the havoc. Its third ability is "Target Lock," which locks the havoc on a single target, causing it to take 30% more damage from the player's units. This makes the havoc a very effective supporter in frontline combat armies, but lacking in the more versatile and defensive abilities of the sentry and energizer. The havoc is also the only variant of sentry which isn't psionic.
The following section contains information from a previous version of StarCraft II which is no longer valid.
Map editor files indicate the havoc may have been called the "monitor" earlier in development. Its Squad Sight and Target Lock abilities are tagged "observer" in the editor files; it is unknown if this was another name used for it at some point, or if the havoc's abilities were intended for the protoss observer, which does not appear in the campaign.