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Commander Adama orders activation of these shields as they fight off the first waves of a Cylon Raider attack on Galactica and her sister battlestars in the opening salvos of the ill-fated Battle of Cimtar (Saga of a Star World). Adama's commands to activate and deactivate the shield are "Positive shields" and "Negative shields", respectively.
Commander Cain also has the shields activated once the basestars begin hitting Pegasus during the Battle of Gamoray. He simply orders "shield", which corresponds to the button that activates the barriers (The Living Legend, Part II).
Electronic defense shields
Electronic defense shields are a defensive capability of Pegasus. In preparation for a direct assault on three basestars, Commander Cain orders "electronic defense shields to maximum power". No visible manifestation of this countermeasure is shown onscreen (The Living Legend, Part II).