Shield guns were Minyan energy weapons.
Jackson and his crew had several of these guns, which they used in their assault on the P7E planetoid. Leela also found a shield gun in the hold of the R1C and used it to blast her way onto the bridge, as well as defend the Doctor and destroy the security devices aboard the P7E.
The guns were worn on the forearm like a shield, with the other hand operating the trigger. The shield part of the weapon was capable of deflecting beams from the similar energy weapons used by the P7E guards. (TV: Underworld)