  In their classical work Caflisch and Sammartino proved the inviscid limit of
the incompressible Navier-Stokes equations for well-prepared data with analytic
regularity in the half-space. Their proof is based on the detailed construction
of Prandtl's boundary layer asymptotic expansions. In this paper, we give a
direct proof of the inviscid limit for general analytic data without having to
construct Prandtl's boundary layer correctors. Our analysis makes use of the
boundary vorticity formulation and the abstract Cauchy-Kovalevskaya theorem on
analytic boundary layer function spaces that capture unbounded vorticity.
