  The Cryogenic Underground Observatory for Rare Events (CUORE) is a ton-scale
cryogenic experiment designed to search for neutrinoless double-beta decay of
$^{130}$Te and other rare events. The CUORE detector consists of 988 TeO$_2$
bolometers operated underground at 10 mK in a dilution refrigerator at the
Laboratori Nazionali del Gran Sasso. Candidate events are identified through a
precise measurement of their energy. The absolute energy response of the
detectors is established by the regular calibration of each individual
bolometer using gamma sources. The close-packed configuration of the CUORE
bolometer array combined with the extensive shielding surrounding the detectors
requires the placement of calibration sources within the array itself. The
CUORE Detector Calibration System is designed to insert radioactive sources
into and remove them from the cryostat while respecting the stringent heat
load, radiopurity, and operational requirements of the experiment. This paper
describes the design, commissioning, and performance of this novel source
calibration deployment system for ultra-low-temperature environments.
