  In this paper we describe the operation and performance of the HERA-B Outer
Tracker, a 112674 channel system of planar drift tube layers. The performance
of the HERA-B Outer Tracker system fullfilled all requirements for stable and
efficient operation in a hadronic environment, thus confirming the adequacy of
the honeycomb drift tube technology and of the front-end readout system. The
detector was stably operated with a gas gain of 30000 in an Ar/CF4/CO2
(65:30:5) gas mixture, yielding a good efficiency for triggering and track
reconstruction, larger than 95 % for tracks with momenta above 5 GeV/c. The hit
resolution of the drift cells was 300 to 320 micrometers and the relative
momentum resolution can be described as: sigma(p)/p (in %) = (1.61 +- 0.02) +
(0.0051 +- 0.0006) p. At the end of the HERA-B running no aging effects in the
Outer Tracker cells were observed.
