TL;DR $600 million mechanically reliable dual-purpose short-to-medium-ranged death ray small enough to mount on technicals enters the arms market 20 minutes into the future. What would war look like then?
20 minutes in the future, Republic of Ruritania revealed their newest air-defense system: the Oxybelas air defense system, according to them, a weapon that will change the face of warfare.
The Oxybelas is a synchrotron particle accelerator and power source (whose origin is jealously guarded by the Ruritanian government) that is small enough to be fitted onto a pickup truck, and yet capable of accelerating a packet of heavy ions to speeds of somewhere around 0.9c, leaving the target with very little warning. Each ion packet, upon striking a target, releases somewhere around 150 megajoules of energy.
The Oxybelas is cooled with an advanced spin-cooling mechanism that cycles liquid nitrogen through the superconductive magnets, enabling a healthy sustained ROF of 6 rounds per minute. The beam itself has an effective range of 30 km before blooming starts to severely degrade performance.
Reliability testing in almost all possible environments have indicated that the Oxybelas air defense system is, curiously enough, as solidly built and mechanically reliable as any current-generation air-defense gun system despite the integration of such radical technology.
The Oxybelas also comes with an integrated phased-array radar, capable of tracking up to 20 targets simultaneously at a range of 40 kilometers. Of course, the Oxybelas is also capable of receiving information from more sophisticated sensors through datalinks, enabling it to fire at any ground, sea, and air targets that the sensors can track.
Of course, such a system has its limitations: namely the per-unit price tag of $600 million.
How would the deployment of such a weapon with its price tag 20 minutes into the future affect 21st Century Warfare as we know it?
Completely forgot about the effects of blooming at short ranges. Air within first 30 km of the beam's path is ionized and pushed out of the way with a "pathfinding" laser before the beam is actually fired.