Any fleet or D-Ships may fire at an opponent at the same world. In RSW Core, D-Ships have the same firepower as ships on orbiting fleets. Specifically, each ship on a fleet gets one shot, and each D-Ship also gets one shot. It takes two shots to destroy each one of your opponent's ships.

Combat and movement occur simultaneously. If a fleet moves away while you fire at it, it only takes half damage.

You cannot simultaneously move and fire a fleet in the same turn.

You may fire an orbiting fleet at D-Ships. If you do this, and fire with at least two more shots than necessary to destroy all the D-Ships, the world will become neutral. The world will remain neutral--unowned by any player--until there is only one player remaining with ships at the world, according to the standard capture rules.