  We present an implementation of the Gehrels et al. (2016) galaxy-targeted
strategy for gravitational-wave (GW) follow-up using the Las Cumbres
Observatory global network of telescopes. We use the Galaxy List for the
Advanced Detector Era (GLADE) galaxy catalog, which we show is complete (with
respect to a Schechter function) out to ~300 Mpc for galaxies brighter than the
median Schechter function galaxy luminosity. We use a prioritization algorithm
to select the galaxies with the highest chance of containing the counterpart
given their luminosity, their position, and their distance relative to a GW
localization, and in which we are most likely to detect a counterpart given its
expected brightness compared to the limiting magnitude of our telescopes. This
algorithm can be easily adapted to any expected transient parameters and
telescopes. We implemented this strategy during the second Advanced Detector
Observing Run (O2) and followed the black hole merger GW170814 and the neutron
star merger GW170817. For the latter, we identified an optical
kilonova/macronova counterpart thanks to our algorithm selecting the correct
host galaxy fifth in its ranked list among 182 galaxies we identified in the
Laser Interferometer Gravitational-wave Observatory LIGO-Virgo localization.
This also allowed us to obtain some of the earliest observations of the first
optical transient ever triggered by a GW detection (as presented in a companion
paper).
