The United States Navy Electromagnetic Railgun.
While this technology will probably cause hell for the people being shelled on the receiving end of it the real potential of this technology is its potential use as a Mass Driver to send objects up into space.
So a little history on this, you see an Artillery Engineer by the name of Gerald Bull proposed some years ago that a gun could be used to propel an object into space thus making the space industry more cost effective and increasing our ability to expand into space. Bull created a project by the name of HARP (No not "that" one) this was the High Altitude Research Project and surprisingly it proved results as Bull managed to get a object 60+ miles into sub orbit. The project sadly was shut down after Canada protested the Vietnam War, the Canadians assuming the project was a weapon wanted no business with it.
Now here's where it gets rather sad and an example of a valuable piece of technology being denied to us due to unforeseeable events. Bull was committed to seeing his project work and in an attempt to get the necessary backing to construct something like a supergun he found his way into Saddam Hussein circle where he was hired as an Artillery designer for the Iraqi military where he began Project Babylon. Bull of course played his cards pretty well in convincing Saddam that he was doing this and not using funds on his own ambitions, he played his cards too well in fact as his projects and occasional work with improving SCUD missiles led many intelligence services to believe he was creating a weapon capable of bombing Israel, he had tried to preempt this by briefing all the intelligence services he could find and arguing how Project Babylon was no threat to Israel or anybody but the damage clearly had been done. Bull had shown himself as a threat and VIP who could not be allowed to escape when the Iraqi War began later Bull was assassinated in his apartment by an unknown shooter thus ending hopes that a Mass Driver capable of sending objects into space would be built.
That is until now. Historically speaking all Wars and Battles have paved the way for advances in Science and Technology, Radar, the Vengeance Weapon Program paving way for modern day Rockets, Atomic Bombs paving the way for Nuclear Energy and now the Electromagnetic Railgun paving the way for a Mass Driver.