Human engineering criteria applicable to the design of helmet mounted displays for use with night vision sensors, such as forward looking infra-red (FLIR) or low light level television (LLTV), are stated and reviewed. Systems requirements are presented which call for pilot operation at night that is as equivalent as practicable to flight under normal daytime visual rules. Requirements are developed that utilize head motion coupled to sensor movement to achieve the semblance of daytime pilotage while conducting operations at night under the cover of deep darkness. At the outset, salient factors are identified and prioritized which are applied to further design tradeoffs leading to helmet mounted visor displays. The prime design objectives being operational suitability, acceptability by the pilot community, reduced crew training requirements and minimal logistics support. In conclusion, alternate design configurations, computer analyses, operating experience, and pilot reaction are cited. Items to be addressed include: overall head supported weight, center-of-gravity, and other ergonomic factors affecting pilot acceptance: such as: comfort, eye-relief, total and instantaneous field of view, full or partial overlap of left-eye and right-eye fields of coverage, and head movement-to-sensor servo response. In addition, items of interest to the operating command: such as: training (ease or difficulty), maintenance of proficiency, and ease of viewing, will be discussed in light of data and operating experience from recently conducted flight trials. Finally, compatibility with nuclear biological and chemical (NBC) defense equipment and requirements, and laser eye protection will be discussed.