A four channel bidirectional wavelength division multiplexing transmission subsystem, including a single channel fiber optic rotary joint (FORJ), was fabricated and characterized.The performance of all the subsystem components is reported over a range of environmental conditions including temperature, shock, vibration, and humidity.Detailed data describing the optical properties of the multiplexers /demultiplexers is correlated with mathematical models representing theoretical multiplexer /demultiplexer performance.The overall system performance is reported in terms of channel losses, channel isolation, BER, and data rate.