  We present results for the first three years of OzDES, a six-year programme
to obtain redshifts for objects in the Dark Energy Survey (DES) supernova
fields using the 2dF fibre positioner and AAOmega spectrograph on the
Anglo-Australian Telescope. OzDES is a multi-object spectroscopic survey
targeting multiple types of targets at multiple epochs over a multi-year
baseline, and is one of the first multi-object spectroscopic surveys to
dynamically include transients into the target list soon after their discovery.
At the end of three years, OzDES has spectroscopically confirmed almost 100
supernovae, and has measured redshifts for 17,000 objects, including the
redshifts of 2,566 supernova hosts. We examine how our ability to measure
redshifts for targets of various types depends on signal-to-noise, magnitude,
and exposure time, finding that our redshift success rate increases
significantly at a signal-to-noise of 2 to 3 per 1-Angstrom bin. We also find
that the change in signal-to-noise with exposure time closely matches the
Poisson limit for stacked exposures as long as 10 hours. We use these results
to predict the redshift yield of the full OzDES survey, as well as the
potential yields of future surveys on other facilities such as the 4m
Multi-Object Spectroscopic Telescope (4MOST), the Subaru Prime Focus
Spectrograph (PFS), and the Maunakea Spectroscopic Explorer (MSE). This work
marks the first OzDES data release, comprising 14,693 redshifts. OzDES is on
target to obtain over a yield of approximately 5,700 supernova host-galaxy
redshifts.
