  The CFHT Large Area U-band Deep Survey (CLAUDS) uses data taken with the
MegaCam mosaic imager on CFHT to produce images of 18.60 deg2 with median
seeing of FWHM=0.92 arcsec and to a median depth of U = 27.1 AB (5 sigma in 2
arcsec apertures), with selected areas that total 1.36 deg2 reaching a median
depth of U=27.7 AB. These are the deepest U-band images assembled to date over
this large an area. These data are located in four fields also imaged to
comparably faint levels in grizy and several narrowband filters as part of the
Hyper Suprime-Cam (HSC) Subaru Strategic Program (HSC-SSP). These CFHT and
Subaru datasets will remain unmatched in their combination of area and depth
until the advent of the Large Synoptic Survey Telescope (LSST). This paper
provides an overview of the scientific motivation for CLAUDS and gives details
of the observing strategy, observations, data reduction, and data merging with
the HSC-SSP. Three early applications of these deep data are used to illustrate
the potential of the dataset: deep U-band galaxy number counts, z~3 Lyman break
galaxy (LBG) selection, and photometric redshifts improved by adding CLAUDS U
to the Subaru HSC grizy photometry.
