It is a device that is being used to control the current of thousands of amps to drive projectile devices such as a rail gun and coil gun.

They come with a solid heat sink and heavy gauge leads. The heat sink is not needed for this application since there is little transfer of heat with these single pulses of typically a few tens of milliseconds. The charging transformer from an ancient TV is bottom left with voltage doubler and relay.

Its SCR drive electronics and protection diodes are placed in the upper centre. And all of it fits with a bit of a squeeze in a lockable glass fronted aluminum case.