  Visible-light long baseline interferometry holds the promise of advancing a
number of important applications in fundamental astronomy, including the direct
measurement of the angular diameters and oblateness of stars, and the direct
measurement of the orbits of binary and multiple star systems. To advance, the
field of visible-light interferometry requires development of instruments
capable of combining light from 15 baselines (6 telescopes) simultaneously. The
Visible Imaging System for Interferometric Observations at NPOI (VISION) is a
new visible light beam combiner for the Navy Precision Optical Interferometer
(NPOI) that uses single-mode fibers to coherently combine light from up to six
telescopes simultaneously with an image-plane combination scheme. It features a
photometric camera for calibrations and spatial filtering from single-mode
fibers with two Andor Ixon electron multiplying CCDs. This paper presents the
VISION system, results of laboratory tests, and results of commissioning on-sky
observations. A new set of corrections have been determined for the power
spectrum and bispectrum by taking into account non-Gaussian statistics and read
noise present in electron-multipying CCDs to enable measurement of visibilities
and closure phases in the VISION post-processing pipeline. The post-processing
pipeline has been verified via new on-sky observations of the O-type supergiant
binary $\zeta$ Orionis A, obtaining a flux ratio of $2.18\pm0.13$ mag with a
position angle of $223.9\pm1.0^{\circ}$ and separation $40.6\pm1.8$ mas over
570-750 nm, in good agreement with expectations from the previously published
orbit.
