The HAVOK tactical nuclear warhead is one of the most powerful ground-based nuclear ordnances in the UNSC arsenal, and has a thermonuclear yield of 30 megatons. The HAVOK is typically detonated via remote signal when not employed as a warhead but in dire circumstances can be activated manually. This is accomplished by twisting the front end of the device, which extends out of the shell, indicating that the device has been armed. When armed using this method the HAVOK will detonate after detection of physical impact with the outer shell.
The HAVOK tactical nuclear weapon is primarily utilized in situations in which the UNSC must eliminate Covenant forces in entrenched in highly defendable locations and formations, or to prevent important locations from falling into Covenant control. The UNSC will authorize the use of HAVOK explosives to eliminate Covenant naval vessels deploying infantry and equipment as well. Nuclear weapons like the HAVOK are employed often in combat against the Covenant Empire, as they are some of the only weapons in the UNSC arsenal capable of directly inflicting catastrophic damage to advanced Covenant technology and massed infantry formations. However, nuclear ordnance is only authorized when all civilian and military populations have been evacuated or compromised within a target area.
Several variants of the HAVOK nuclear device have been developed for use in different tactical situations. These include the HAVOK mine and the Variant V HAVOK. The Variant V HAVOK is designed to maximize the thermonuclear yield in the vacuum of space. The Variant V HAVOK is a warhead that is mounted within a missile to be launched from ground-based silos or naval vessels.
On February 12, 2535, UNSC NavSpecWar deployed three teams of Spartan-II commandos on Jericho VII to combat Covenant forces invading the colony. At one point during the engagement Red Team was successfully able to plant a HAVOK Nuke near a Covenant rally point where a Cruiser was to deploy ground forces.
In October–December 2552 multiple HAVOK Nuclear Weapons were used during the Battle of Earth, a notable use was around October 21, 2552, when Blue Team was deployed to Mount Erebus in the Antarctic to destroy a Covenant excavation force using a HAVOK.
In 2557, when the Ur-Didact attacked Ivanoff Research Station near Installation 03 in order to retrieve the Composer, John-117 searches for a way to destroy it and ultimately decides to use the station's seven excavation-grade HAVOK mines to destroy the Composer and deny the Didact his weapon. But before the nukes are ready, the Didact succeeds in acquiring the Composer; digitizing everyone in the station before departing for Earth. John-117 follows in a Broadsword armed with one of the HAVOKs in a missile and ultimately boards the Didact's ship and detonates the nuclear weapon manually, destroying both the ship and the Composer. The only survivor is John-117 himself, shielded by Cortana at the last moment with a hard light bubble at the cost of her own "life."
During the Second Battle of Requiem, Jul 'Mdama's Covenant forces placed stolen HAVOK nukes in the server and engine rooms of the UNSC Infinity. These nukes had been adapted with active camouflage. They were disarmed by Fireteam Crimson before they could be detonated.
- The HAVOK nuclear warhead shares its name with the HAVOK physics engine used in the Halo games. However, Halo: The Fall of Reach, which introduced the warhead, was published in 2001, whereas the HAVOK physics engine was not implemented into the series until Halo 2, which was released three years later, so it is unlikely that the warhead was named after the physics engine.