  In 2018-2019 the VERITAS VHE gamma-ray observatory was augmented with
highspeed optical instrumentation and continuous data recording electronics to
create a sensitive Stellar Intensity Interferometry (SII) observatory,
VERITAS-SII. The primary science goal of VERITAS-SII is to perform stellar
diameter measurements and image analysis in the visible wavebands on a
selection of bright (m< 6), hot (O/B/A) stars. The VERITAS Collaboration has
agreed to the deployment and operation of VERITAS-SII during several days each
month around the full moon period when VERITAS does not perform VHE gamma-ray
observations. The VERITAS-SII augmentation employs custom high-speed/low-noise
focal plane instrumentation using high quantum efficiency photomultiplier
tubes, and a battery-powered, fiber-optic controlled High Voltage supply. To
reduce engineering time, VERITAS-SII uses commercially available high-speed
(250 MS/sec), continuously streaming electronics to record the time dependence
of the intensity fluctuations at each VERITAS telescope. VERITAS-SII also uses
fast ( < 100 psec) data acquisition clock synchronization over inter-telescope
distances (greater than 100 m) using a commercially available White Rabbit
based timing solution. VERITAS-SII is now in full operation at the VERITAS
observatory, F.L.Whipple Observatory, Amado, AZ USA. This paper describes the
design of the instrumentation hardware used for VERITAS-SII augmentation of the
VERITAS observatory, the status of initial VERITAS-SII observations, and plans
for future improvements to VERITAS-SII.
