Exactly. You'd need a small nuclear power plant for anything of substantial power.
And maglev technology is awesome.

Originally Posted by Spartacus

Maglev trains are based off the same concept of rail guns. They are incredibly efficient and work well.

However, as a military application, electromagnetic-based weapons are simply not feasible due to power requirements and resulting weight.

Not saying they dont exist... just saying it is unlikely to.

That was my thought, have they been incorporated into a ship, which is probably the most portable thing with the potential to generate the power.

Yeah,power requirement is a big issue for those.

I had heard that the US Navy wanted to have a prototype on a ship by 2012 but that has been moved back to 2020 because of issues related to over heating caused by "firing" the weapon multiple times. Apparently the development of proper insulation and heat spreaders is years behind schedule, which one would think the insulation would be the easy part compared to say firing a 7kg projectile 200 miles without the use of black power. The Navy has moved away from steam catapults though and is using a magentic rail system similar to what you'd get on your maglevs in Europe.

7 kg? 200 miles? Unless it's guided, don't count on much accuracy.
Though I think that MagLev is a great idea for launching jets off of carriers.

The US wants to mount them on the Zumwalt class destroyers. They are around, give it another Decade.

It's going to be a very, very long time before you see rail or Gauss guns mounted on anything smaller than a warship. I know they have plans for a man-portable gasdynamic laser - but only plans. There's not even a prototype yet, it'll be decades before there is a power supply powerful and light enough to make it at all practical.