  The Karl G. Jansky Very Large Array (VLA) is currently the world's most
powerful cm-wavelength telescope. However, within a few years this blanket
statement will no longer be entirely true, due to the emergence of a new breed
of pre-SKA radio telescopes with improved surveying capabilities. This white
paper explores a region of sensitivity-area parameter space where an investment
of a few thousand hours through a VLA Sky Survey (VLASS) will yield a unique
dataset with extensive scientific utility and legacy value well into the SKA
era: a deep full-polarization L-band survey covering a few square degrees in
A-configuration. Science that can be addressed with a deep VLASS includes
galaxy evolution, dark energy and dark matter using radio weak lensing, and
cosmic magnetism. A deep VLASS performed in a field with extensive
multiwavelength data would also deliver a gold standard multiwavelength catalog
to inform wider and shallower surveys such as SKA1-survey.
