  We describe the MERger-event Gamma-Ray (MERGR) Telescope intended for
deployment by ~2021. MERGR will cover from 20 keV to 2 MeV with a wide field of
view (6 sr) using nineteen gamma-ray detectors arranged on a section of a
sphere. The telescope will work as a standalone system or as part of a network
of sensors, to increase by ~50% the current sky coverage to detect short
Gamma-Ray Burst (SGRB) counterparts to neutron-star binary mergers within the
~200 Mpc range of gravitational wave detectors in the early 2020's. Inflight
software will provide realtime burst detections with mean localization
uncertainties of 6 deg for a photon fluence of 5 ph cm^-2 (the mean fluence of
Fermi-GBM SGRBs) and <3 deg for the brightest ~5% of SGRBs to enable rapid
multi-wavelength follow-up to identify a host galaxy and its redshift. To
minimize cost and time to first light, MERGR is directly derived from
demonstrators designed and built at NRL for the DoD Space Test Program (STP).
We argue that the deployment of a network that provides all-sky coverage for
SGRB detection is of immediate urgency to the multi-messenger astrophysics
community.
