As the technology used to wage warfare has advanced, all new weapons and tactics have risen to use them. In the process, previous methods become far less prominent, and often eventually disappear altogether. Most modern navies have all but abandoned battleships, and the only blades today's soldiers carry are knives. But in the future... what if technology takes a sudden and (un?)expected turn? The advent of military-grade lasers and fire-control systems that are decidedly not Point Defenseless makes missiles useless and taking aircraft into battle suicidal. All those modern aircraft carriers and missile cruisers suddenly become obsolete, and the battleship is king of the seas once more. What if personal-scale Deflector Shields make swords and spears viable weapons again? This occurs a lot in Speculative Fiction, where some discovery or advance in science or technology has the net effect of rendering the last 20 to 200 years of military tactical development moot, forcing a return to the methods of an earlier time of warfare, often still with high-tech spins on the old gear. For example, if large close-combat weapons become viable again, they may develop Laser Blades, Hot Blades, or Vibroweapons. This overlaps with Retro Upgrade. See also Break Out the Museum Piece, when this happens in a more immediate sense.
Examples:Anime & Manga
- Mobile Suit Gundam introduced the Minovsky Particle, which when scattered across an area did a number on detection and guidance equipment, forcing both land and space combat back into visual ranges. It should be noted that the arming of the Zaku II with a Heat Hawk was something of a predictive move, with Zeonic designers figuring that the Federation would develop their own mobile suits sooner or later, and added the weapon just in case.
- Mobile Suit Gundam SEED has "Neutron Jammers", which prohibit fission reactions and jams radios. The result: no nukes, everything runs on batteries, and, you guessed it, close-range combat.
- CoDominium: To keep the the status quo, the titular Soviet-American alliance has banned most research. While their Space Navy hasn't suffered (being needed to colonize and police the stars), the restrictions has caused a regression in ground combat. Improvements to computer countermeasures, railguns, and man-portable missiles have made aircraft obsolete. Improvements to body armor has limited effective sizes of ammunition. 21st Century warfare resembles early 20th century combat. In addition, the colonial worlds lack industry, so very few can build tanks or artillery. Unless it's a CD Marine outfit or a merc company from one of the richer planets, often battles on colonial worlds are infantry only.
- Hammers Slammers: Thanks to accurate targeting and Powerguns, aircraft has practically disappeared from the field of battle. Artillery fire can be interdicted by powergun blasts, but shells still manage to get through. Nukes are rendered useless thanks to "nuclear suppression fields". In the backstory, tanks themselves almost disappeared from the battlefield due to developments in technology — man-portable anti-tank rockets, pin-point accurate missiles, and helicopters that could strike rapidly all made tanks rapidly obsolete until fusion and powerguns made them practical again.
"Technology had dragged the tank to the brink of abandonment. Not surprisingly, it was technology again which brought the panzers back."
- In the Childe Cycle's first book, Dorsai!, long range countermeasures have actually reduced the effectiveness of many weapons. Civilians have better, more advanced firepower than most soldiers. As a result, many troopers rely on simple, effective weapons.
- Dune has "Holtzman fields", which radically changes war. Artillery is obsoleted, most projectile weapons can't penetrate the field, and even lasguns can't be used due to "explosive pyrotechnics". As a result, ground combat is relegated to sword combat. The exception is found on the titular planet — shields attract Sand Worms, and as such can't be used for the most part, causing warfare on Arrakis (Dune) to shift back the other way. This spreads to the rest of the empire in God-Emperor of Dune when shield technology is banned.
- In the Legacy of the Aldenata, the invading Posleen have point-defense strong enough to neutralize our missiles and aircraft. Necessitating the revival of battleships on sea and "land ships" on land with a lot of armor and big guns.
- Impeller drive in the Honorverse places an impenetrable field right above and below starships, meaning that ships can only be hit in two dimensions or conversely fire from those same sides, thus broadsides in 3-d space.
- In World War Z, the military has abandoned tanks, jet fighters, aircraft carriers and indeed most modern tactics. Assault rifles, grenades and bayonets have been replaced - the infantryman's new weapons of choice are a semi-automatic rifle and the "Lobotomizer", a cross between a shovel and a battleaxe. The squad is also no longer the base unit for organization of men - men are organized into lines and fire in accurate, devastating salvos. Zombies have rendered modern military equipment and tactics obsolete in favour of the kind of things you'd expect from an Napoleonic battlefield.
- Played with in the Book of the New Sun. With most of Urth's technology has regressed, so most soldiers are armed with crossbows and slings, while others have lances. Crossbows and slings that have pyrotechnic ammunition, and lances that can fire bolts of energy.
- Mutant Chronicles: When the Dark Symmetry (a cosmic horror force) is released, advanced computers become evil and electronics become unreliable. As a result, warfare (and pretty much everything else) regresses to The Seventies.
- In Warhammer 40,000, though modern weaponry has not been replaced, melee combat is back again as regular fare on the battlefields with exclusively melee-range weapons being commonly deployed, but there is no single specific reason for this having happened (aside from the expected Rule of Cool of course) - the rulebook words it implying close-combat likely renders troops unable to shoot their guns despite Pistol-Whipping being perfectly usable to give yourself an opening to fire in a melee. However, many assault troops employ Sword and Gun to get something of a best of both worlds in close-combat, though there is certainly individual troops who use only melee weapons for arming themselves.
- And the fact that when you're a hulking monstrosity, a psychic bullet-dodging alien, or a daemon from Hell, and your enemies are Puny Earthlings, close combat isn't that stupid of an idea. Likely expecting them to try it, the Puny Earthlings have Bayonet Ya as standard-issue though being Puny Earthlings against the aforementioned opponents, it doesn't especially help their odds when their enemies get close enough.
- The old Manhunter universe had swordsmen who specialized in fighting aboard spacecraft, where guns are impractical because of the tendency of stray bullets to punch holes in the hull and/or destroy necessary equipment.
- In BattleTech, warfare is dominated by Battlemechs and lasers are commonly used as weapons. However the first two Succession Wars have knocked back most Inner Sphere's technological progress resulting in most fights limited to close range combat. The Clans however possess more advanced technology than the IS but they intentionally made most of their fighting limited to honor duels, to hone their skills and limit their losses.
- Command & Conquer 3: Tiberium Wars has GDI revert back to using tanks, since it was just more cost-effective. It turns out Mecha and hover tanks are too expensive to maintain. Similarly, Nod ends up abandoning subterranean burrowing vehicles due to environmental changes.
- Averted in the Dune II and Emperor: Battle for Dune games. Unlike the books (shield technology makes many projectile weapons obsolete), the various factions operate tanks, artillery, and machine guns just fine. Dune II has benefit of being set on Arrakis, where Shields are avoided to prevent the major local wildlife from going berserk. But in Emperor, all units are still usable even not on Dune, and House Ordos still uses some shielded units on Arrakis.
- In Metal Gear Rising: Revengeance CNT armour makes cyborg infantry nearly Immune to Bullets, so melee Vibroweapons have come back into fashion.
- In the Big Head Press comic Phoebus Krumm, "S-fields" enable FTL travel but disable all electronics within the field, making space warfare essentially age of sail naval combat.
- In the future of S.S.D.D advances in anti-air defense had made air and missile strikes nearly impossible, and fullerene armor made ordinary guns obsolete. Which meant most battles were fought on the ground, by men in suits armor hitting one another with hammers. "Oh, how far we have come." One of the major story arcs involves a war that ends when one side uses a Kill Sat to knock out their opponent's AA and launching a bunch of museum piece ICBMs