MFTF-B is the largest fusion mirror device currently under construction. When completed in 1988 the mirror will be fueled and heated by 11 neutral beamlines whose combined power output will be over 40 MW. These beamlines are being designed and built by TRW Systems. Associated with each beamline is a vacuum system whose performance plays a crucial role in the operation of neutral beams. Good vacuum is needed in the injectors and dump tanks to limit the beam loss due to reionization and to avoid excessive gas flow into the plasma chamber. This paper will describe the design of these vacuum systems and explain the considerations and tradeoffs made in the process.