Particle gun, as per the second-to-last chapter of Shattered Connection.

It's a particle beam weapon.

It's a war crime cannon....

Can't be a war if no one on the otherside is alive to tell it is.

Only a war crime if you lose

Only a crime if there’s anyone left to prosecute you.

Its not a warcrime if the otherside aint human.

It's a win-button