The ACCESS Ocean Model (ACCESS-OM) 20^th century climate is evaluated through a series of international inter-comparison studies: variability of the Atlantic Meridional Overturning Circulation; global and regional thermosteric sea level rise; the dynamics and watermass transformation in the Southern Ocean; and the ocean and sea-ice interactions in the Arctic Ocean. ACCESS-OM comprises the U.S. NOAA/Geophysical Fluid Dynamics Laboratory Modular Ocean Model (MOM4p1), the U.S. Los Alamos National Laboratory CICE4.1 Sea Ice Model, and the French CERFACS OASIS3.2.5 coupling software. Our simulations contribute to a series of studies known as Coordinated Ocean-ice Reference Experiments (COREs) through the WCRP/CLIVAR Working Group on Ocean Model Development. The CORE Inter-Annual Forcing (CORE-IAF) hindcasts use the atmospheric forcing of Large and Yeager to simulate the period 1948-2007. NCEP/NCAR Re-analysis atmospheric fields are modified with observationally based corrections, and use a standard set of bulk formulae representing ocean-atmosphere boundary fluxes. Results from the ACCESS Ocean Model simulations are benchmarked against up to 17 other international global ocean climate models that participate in the CORE intercomparisons. This broad ranging intercomparison study allows a frank assessment of what ocean climate features of the ACCESS model are truly world class, and more importantly, where future model development effort for further improvements in the simulations should be focussed.