- This article is about the word. For the RPG sourcebook, see LosTech: The MechWarrior Equipment Guide.
A portmanteau word of lost (or loss of) technology, the term Lostech in the BattleTech universe generally refers to applied technological advances and knowledge that existed during the Star League era, but which were lost in the Succession Wars that followed. It is typically used as an adjective, but can also be used as a noun (often spelled LosTech). As a noun, it can either denote an item that is associated with lostech, or refer to LosTech as a concept or historical event or situation—the technological decline of humanity as it occurred throughout the Succession Wars.
As a defining aspect, LosTech cannot be produced anymore under current technology levels, except occasionally by automated facilities which are invariably LosTech themselves. Often, the working principles of lostech items are not even understood anymore and the secret of their production is lost. This became a growing problem when more and more vital industry, including automated factories, collapsed from maintenance shortfalls, either because nobody knew how to properly maintain the mysterious machinery or simply for a lack of spare parts. In the dark days of LosTech, only scavenging and improvisation kept any advanced technology working at all.
Many lostech items function without requiring the user to actually understand how or why they function. This has given rise to the religious attitude some display towards advanced technology, seeing it as a sort of magic, and to the evolution of ComStar from a telecommunications provider to a religious order, including the establishment of the 'Word of Blake' as an accepted religion. Many ComStar adepts actually believe that their prayers are just as important for the proper operation of machinery as operations procedures from the manual. The concept of "repair prayer" has become a running joke that some still take very seriously.
 History of the technological decline
As a concept, LosTech is often used to describe the loss of technological knowledge over the course of war.
 Bombing back into the stone age
In the early Succession Wars, all parties deliberately sought to destroy the enemy infrastructure. Amidst the overall ruthless mayhem that obliterated entire worlds, factories, shipyards and star-ships were prime targets. Humanity as a whole literally bombed itself back into a proverbial 'stone age,' and the Successor Lords realized too late that the damage was beyond repair. On many worlds, the developmental level had fallen back to the level of 20th-21st century science and technology, or even to primitive tribal communities without space flight, subsisting on farming and manual labor with medieval technology levels.
 Preserving Lostech
When it became apparent that the ability to build and maintain essential technologies was fading away quickly, irreplaceable civilian assets became regarded as non-combatants through an informal agreement. ComStar was accepted as a neutral caretaker of the interstellar communication network, and then gradually of advanced technology in general. As lostech items, even those of strategic value, were generally kept out of the fighting, combat became more and more ritualized in the fashion of medieval battles or even duels over the course of the Succession Wars. In order to prevent further damage to urban or industrial areas, battles were arranged in outlying regions. Defeated opponents were allowed to withdraw, and captured MechWarriors were ransomed. This development went hand in hand with the establishment of neo-feudal societies, also reminiscent of the middle ages.
Still, the wars raged on. Although infrastructure was not a designated target anymore, collateral damage still occurred and by the early 31st century, many vital technologies were LosTech. Complex systems such as BattleMechs, JumpShips or Hyperpulse Generators became lostech as a whole as most of their individual components such as Fusion Engines or Kearny-Fuchida Drives became increasingly unavailable, difficult to maintain and near impossible to produce. Many colonies were doomed because declining shipping deprived them of their food and supplies imports, others because vital life support technology such as water and air purification systems failed or were destroyed, rendering whole worlds uninhabitable.
 Holy Shroud
An aggravating element was ComStar, who evolved into a mystical, pseudo-religious order. They pursued a secret agenda and actively sought to quell technological rediscoveries and advancements in the Successor States, because they felt they alone should have control over advanced technologies for their ultimate goal to guide mankind to the light. In this they went so far as to wage a clandestine war against all other factions' technology, culminating in Operation Holy Shroud, a series of murders and sabotage aimed at the brightest scientists and facilities outside of the order. There were numerous similar operations, including the Tripitz Affair and Operation Holy Shroud II, but ComStar was careful never to reveal their hand in any of these.
All major factions realized the importance of rediscovering lost scientific knowledge, and several research facilities were established in an effort to recover some of the lost technologies.
 The NAIS
On Halstead Station, Hanse Davion's troops managed to retrieve many books from the library of an ancient, forgotten Star League university in 3013. The so-called Halstead Collection of books prompted Prince Davion to allocate considerable funds to the creation of the New Avalon Institute of Science (NAIS). With the headstart in knowledge from the Halstead Collection, the NAIS became the premier scientific institute outside of ComStar, covering a wide field of sciences.
 The Helm Memory Core
The recovery process was helped along significantly following the recovery of a Star League library core on the planet Helm by the Gray Death Legion in 3028 and its subsequent dissemination throughout the Inner Sphere. Aware of deliberate attempts to destroy the memory core and suspicious of ComStar's role, Grayson Carlyle deliberately handed out free copies to independent traders in an attempt to spread the invaluable knowledge without involving ComStar.
For the first time in centuries, technology was on the rise again, and an upswing made itself felt throughout the Inner Sphere. However, with the gradual rediscovery of lost technology, its sacrosanct status eroded away. Military commanders were increasingly prepared to accept crippling losses to their 'Mech and armor units, knowing that once again, they could be replaced.
 Clan invasion
When the Clans invaded in 3050, the Inner Sphere became yet more motivated to recover lost Star League technology to counter the invaders' technological advantage, and an influx of Clan technology provided another technological boost. In addition, the mutual threat of the Clans enforced a hitherto unknown level of cooperation between the individual successor states. Technology exchanges and envigorated trade further accelerated the rediscovery of lost technologies and even the evolution of a few new ones.
It seemed as if LosTech could be overcome after all. By the 3060s, the Inner Sphere had re-established a technological knowledge base that approximated the technological state of the Star League era, with more than a few advances beyond what even the Star League had developed at its height. However, due to the thoroughly ramshackle state of their ailing industries, application of recovered knowledge was lagging behind the technological improvements by a long shot, and a grossly disproportionate amount of the advances were by necessity concentrated on military technology as opposed to more general breakthroughs. Overall, the Clans still enjoyed roughly two centuries of technological advancements over the Inner Sphere who was catching up, albeit slowly.
The pendulum swung backwards again in 3067, when the ultra-reactionary ComStar splinter faction, Word of Blake, launched their Jihad across known space. With the deliberate objective to quell the technological advance, and to pit as many factions against each other as possible, they used sabotage, orbital bombardments and weapons of mass destruction on a grand scale to undo the hopeful developments of the previous decades.
When the dust settled after the Jihad, many industries across the Inner Sphere had been devastated by the intense fighting. With the subsequent formation of the Republic of the Sphere and Devlin Stone's demilitarization of the new nation, many arms producers in the Republic made 'sword-to-plowshare' conversions. IndustrialMechs experienced a rise in mainstream applications during this period of relative peace.
 Dark Age
However, the Republic would face a new technological setback when 80% of the interstellar HPG communications network was rendered inoperable in 3132 by a concerted effort including system viruses, sabotaged components, and coordinated attacks against ComStar facilities. These events pushed humanity back into its darker days and set the stage for what is called the Dark Age, where LosTech once again haunts humanity.