  The third flight of the High-Resolution Coronal Imager (Hi-C 2.1) occurred on
May 29, 2018, the Sounding Rocket was launched from White Sands Missile Range
in New Mexico. The instrument has been modified from its original configuration
(Hi-C 1) to observe the solar corona in a passband that peaks near 172 Angstrom
and uses a new, custom-built low-noise camera. The instrument targeted Active
Region 12712, and captured 78 images at a cadence of 4.4 sec (18:56:22 -
19:01:57 UT; 5 min and 35 sec observing time). The image spatial resolution
varies due to quasi-periodic motion blur from the rocket; sharp images contain
resolved features of at least 0.47 arcsec. There are coordinated observations
from multiple ground- and space-based telescopes providing an unprecedented
opportunity to observe the mass and energy coupling between the chromosphere
and the corona. Details of the instrument and the data set are presented in
this paper.
