As Ovid, Roman poet and general good guy, once observed:
Clever human nature, victim of your own inventions, disastrously creative, why cordon your cities with towered walls? Why arm for war?
I suspect that for the vast majority of human history, the answer to this question has been some variation of "because we can" or alternatively, "It's cool". And in that spirit, I present to you The Rail Gun.
In case you missed it, that was the air actually catching on fire due to the intense speed of the rail gun round.
Using giant electromagnets, the rail gun accelerates a metal projectile to an insanely fast 8,270 feet per second. That's 5,640 mph, or 9,076 kph. Something travelling at that speed doesn't need to explode- the energy it transfer to the target does more than enough damage.
So why has the US Navy built this awesome/scary/awesome again weapon? From Gizmodo:
The Navy is researching rail guns because they would weigh less than conventional ones, and since they rely on electromagnetics to fire rounds, you wouldn't need a big, dangerous pile of explosives stored in a magazine. All of that means a lighter ship, and a much more deadly ship: a combat-ready rail gun would be able to fire Mach 5 projectiles over 200 miles with pinpoint accuracy, hitting 5 meter targets.
Or, because it makes cool video.