S0E20 : Razor (2)

Admiral William Adama assigns the Pegasus to find a Raptor that vanished during a scientific-research mission. At the Raptor's last known location, an armada of antiquated Cylon Raiders piloted by Centurions attacks the Pegasus. The captive Sharon identifies the old-fashioned machines as "guardians," a particular group of Cylons who experimented on humans during the first Cylon War.