  We report the detection of very high energy gamma-ray emission from the
blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging
Telescope Array System (VERITAS). VERITAS observations of the source were
triggered by the detection of a hard-spectrum GeV flare on May 15, 2015 with
the Fermi-Large Area Telescope (LAT). A combined five-hour VERITAS exposure on
May 16th and May 18th resulted in a strong 13$\sigma$ detection with a
differential photon spectral index, $\Gamma$ = 3.8 $\pm$ 0.4, and a flux level
at 9% of the Crab Nebula above 120 GeV. This also triggered target of
opportunity observations with Swift, optical photometry, polarimetry and radio
measurements, also presented in this work, in addition to the VERITAS and
Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period
finds evidence of a shortest variability timescale of $\tau_{obs}$ = 6.2 $\pm$
0.9 hours, indicating emission from compact regions within the jet, and the
combined gamma-ray spectrum shows no strong evidence of a spectral cut-off. An
investigation into correlations between the multiwavelength observations found
evidence of optical and gamma-ray correlations, suggesting a single-zone model
of emission. Finally, the multiwavelength spectral energy distribution is well
described by a simple one-zone leptonic synchrotron self-Compton radiation
model.
