The droid marine, like all other droids designed by Baktoid Combat Automata, was used for combat against the Republic Navy. Bearing green markings on their skeletal forms, droid marines were equipped with a standard battle droid E-5 blaster rifle, E-60R missile launcher, and supplied with four thermal detonators. They also carried a "backpack" like object with them, similar to their B1 counterparts. They had the ability to pilot ships, but their primary function was to either defend their capital ship, or board an enemy ship. They were almost never seen on the ground.
Serving as a Separatist capital ship's last line of defense against clone boarders, they were also useful for boarding the Republic's Venator-class Star Destroyers and destroying them from within. They penetrate the inner workings of a Republic vessel and blow up the shield generator, letting a CIS cruiser destroy the star destroyer. Droid marines almost proved themselves as worthy opponents for the Clone marines and Pilots of the Clone Army. They could board by landing in the hangar of an enemy cruiser. After the execution of the Separatist Council, these units were de-activated. However, some would be used by the separatist fugitive Gizor Dellso in the Battle of Mustafar.
Droid Marines could only be used in Space Battles in Star Wars: Battlefront II.