A Defence Laser is a very large Imperial laser weapon commonly used as a static, planet-based, anti-starship defence by Imperial Planetary Defence Forces. Due to its power consumption and sheer weight, it cannot be installed on a ground vehicle of standard size.
The Defence Laser is normally only mounted on fixed emplacements or extremely large vehicles such as a Battle Titan. The immense Imperator-class Titan is capable of mounting one as an anti-aircraft weapon.
The average length of a Defence Laser's main lasing chamber is over 15 metres, with an overall weight of many tons. A Defence Laser is of little use against ground-based targets, as its practical minimum range was nearly a Terran mile at ground level.
The largest Defence Lasers use vast reservoirs of plasma-based energy, blacking out local power grids for kilometres around their emplacements each time they fire. The blinding red blasts unleashed by a Defence Laser are so powerful that they can breach the atmosphere of a planet and engage targets in low orbit, making the weapon invaluable for repelling alien invasions or other planetary assaults.
Even a glancing blow from a Defence Laser can be enough to drive off any voidship up to cruiser-class in size once the vessel's Void Shields are brought down. A smaller escort vessel may even be cut in two by the blast if struck by a direct hit.
These massive laser weapons, housed in extensive installations on planetary surfaces, are classified as Lance weapons by voidship standards. Although able to project their powerful beams hundreds of kilometres outside of the planet's atmosphere, planet-based lasers require even more power than ship Lances to compensate for the diffraction of the energy beam caused by firing through the atmosphere.
These power requirements can be satiated by on-site generatoriums, or by drawing from the power grid of the planet's infrastructure. In many cases, the bulk of the defence laser silo's supporting machinery is built underground, adding the protection of hundreds of feet of rock to the metres-thick armored walls of the facility above.
- Duty's Fist - Duty's Fist was the Defence Laser deployed to protect the west gate of the city of Bellephon upon the world of Thesus Reach, and employed technology dating back to the Dark Age of Technology. The Fist could reroute the power supplies of the entire metropolis into one earth-shattering laser blast. When fired in this manner, Duty's Fist possessed the capability to shatter a Battle Titan into a thousand pieces and even engage targets in orbit above the planet. During the battle for Bellephon when the Forces of Chaos assaulted Thesus Reach during the 13th Black Crusade, Duty's Fist exchanged fire with the Planet Killer, Abaddon the Despoiler's personal flagship. Though it forced the Planet Killer to undertake evasive manoeuvres, it was eventually disabled by a powerful Greater Daemon of Tzeentch, and its defenders were torn apart by a one-man assault by Kharn the Betrayer, Champion of Khorne.
- Hammer of the Cursed - A Defence Laser with over 20 confirmed enemy kills.
- Spear of the Emperor's Fury - A Defence Laser with over 20 confirmed enemy kills.
- Eternal Vigilance - A Defence Laser with over 20 confirmed enemy kills.
- Inescapable Wrath - A Defence Laser with over 20 confirmed enemy kills.
- Pious Retribution (called "Gunhead" by its crew) - A Defence Laser with over 20 confirmed enemy kills.
- Battlefleet Gothic: Ships of the Gothic Sector, "Low Orbit Defences," pg. 146
- Apocalypse Datasheet (Link Defunct)
- Warhammer 40,000: Rogue Trader (1st Edition), pg. 87