INTRODUCTION General The increasing need for the internal carriage of weapons and stores on combat aircraft in response to the dual requirements of low drag and low radar signature has created the need for information on weapons bays with doors. During weapon deployment the bay is necessarily open to the effects of the external flow@ which creates an unsteady flow environment both within and around the bay. Such flows can engender not only aerodynamic problems in terms of increased drag and potential difficulties with weapon deployment@ but also structural and acoustic problems related to the high intensity tones that can be generated. These structural and acoustic problems can affect the design of both the bay and its contents B on-board avionics for navigation and guidance can be seriously affected by intense acoustic tones and the random vibrations induced by the unsteady flow. The vibrational environment alone requires special design standards for equipment in aircraft@ see References 53@ 54@ 56 and 57@ and spacecraft@ see Reference 55. Although weapons bay design is the main area in which cavity data are required@ other areas@ such as undercarriage bay design@ can also benefit from the use of such data. Obviously@ the geometry of weapons and undercarriage bays will vary according to each application@ but a reasonable@ albeit idealistic@ shape to assume is a rectangular planform cavity B most researchers have made this assumption@ and it is the configuration adopted in this Data Item. That is not to say that other configurations are not required; indeed other planform shapes@ such as elliptical@ have been tested and require study in their own right.