WDM systems are being installed as a means to realise higher capacity, however, most of these WDM networks have an individual channel capacity of up to 2.5 Gbit/s. Initially WDM systems based on 4 wavelengths were deployed, 16 wavelength systems are now readily available with 32 wavelengths and above becoming available with further expansion planned. The maximum number of possible wavelengths is currently limited by the optical amplifier bandwidth. Based on the ITU channel spacing of 100 GHz and today's state of the art optical amplifiers a maximum of approximately 40 channels can be envisaged, giving a maximum transmission capacity of 100 Gbit/s at 2.5 Gbit/s per channel. In order to increase this capacity further it will be necessary to raise the individual channel bit rates beyond 2.5 Gbit/s. Alternatively reduced channel spacing can be used although this will require enhanced component specification and reduced system performance tolerance, this will therefore increase overall system cost. We explain the implementation of a 32 wavelength system where the single channel bit rate can be up to 10 Gbit/s. Although much higher bandwidths have been achieved in the laboratories this 320 Gbit/s capacity is at the leading edge in terms of public network transmission systems.