A HUD system for external attachment to a helmet. The system has an enclosure adapted to house a graphics processing unit, communications device and an optical system for generating the HUD display. The optical system has a display and a light guide adapted to guide light from the display from an input to an output where the HUD is presented in the view of the helmet user. The input of the light guide is located internal to the enclosure and the output of the light guide is located external to the enclosure.