The two models of the Mk 37 NVS differ basically by the type of mount used. Mod 1 is mounted on a tripod,  and  Mod  3  is  bracket-mounted  on  the  ship's signal bridge railing. The tripod mount supplied with the Mod 1 consists of three adjustable legs with a tripod adapter on top to secure the sight to the mount. The bracket mount for the Mod 3 is approximately 6 inches by 4 inches by 3.5 inches and is used when installing the sight at a suitable viewing location. The bracket mount is capable of positioning the Mk 37 Mod 3 through 360 degrees in train and from -28 degrees to +44 degrees in elevation. The Mk 37 consists of three functional sections: objective  lens,  image  intensification  tube,  and  eyepiece. The  objective  lens  assembly  consists  of  lens elements   and   mirrors,   which   function   optically together and focus the image. The assembly is purged and sealed in an atmosphere of dry nitrogen to prevent lens fogging. The  image  intensification  tube  consists  of  three stages of fiber optics, each with a photocathode and phosphor  screen  amplifying  and  transferring  the image  to  the  next  stage.  The  adjustment  for  the intensifier is set at installation to prevent damage to the intensifier tube and must not be disturbed. The eyepiece assembly consists of glass elements that function to magnify and focus the image on the eye of the operator. The Mk 37 NVS has seven glass elements in each eyepiece. The eyepiece assembly is purged and sealed in an atmosphere of dry nitrogen to prevent fogging. The Mk 37 NVS is supplied with a monocular eyepiece; attached to the eyepiece is a rubber eyeshield, which protects the eyes and aids in security by covering the areas around the eye. Light leaks are thereby prevented. In addition to the monocular eyepiece lens, the Mk 37 NVS is supplied with a binocular eyepiece lens. This lens allows the observer to use both eyes, thereby reducing eye fatigue. The binocular eyepiece allows a small amount of backglow from the image tube to illuminate the operator but is acceptable for  most  surface-ship  applications. A power converter is supplied with the NVS for convenience in use aboard ship or whenever 115-Vac, 60-Hz  power  is  available.  The  power  converter consists of the converter unit and cord assembly. It is sealed in a plastic cylindrical case in a threaded metal cap and is not repairable. The input connector of the converter is on the cap end, and the output spring contact is on the other end. The converter unit screws into the battery case of the NVS after the battery has been removed. The 20-foot cord has a converter plug on one end and a standard shipboard 115-Vac, 60Hz power plug on the other. If the entire cord is not required to reach the power source, roll up the excess to avoid creating a walking hazard. A BA 1100/U 6.8-volt  disposable  mercury  battery  is  also  supplied with   the   NVS.   The   battery   has   a   72-hour continuous-use life-span and a 2-year shelf life. The battery is placed in the main housing with the positive end first. The positive end is easily identified, even in the dark, by its slightly raised center. Operation Before operating the Mk 37 NVS, the operator needs knowledge and skill in the installation and setting up of the equipment. Actions required prior to installation are as follows: 1. Relieve air pressure inside the carrying case by pressing the core of the relief valve, located near the carrying handle, before releasing the latches. 2. Cut wire seals by all case latches. 3. Release all case latches and remove the cover. 4. Inventory and inspect the contents to ensure they are ready for installation. Installation of the NVS consists of mounting the sight  on  the  appropriate  operational  location  and installing the power converter or battery. Locate the NVS at two positions, one port and one starboard. Ensure 360-degree rotation and that the location provides ample clearance for operation of the sight in al1 positions of train  and  elevation  without  interference. The setup consists of removing the NVS from the storage case. Secure the pintle in the bracket and locking assembly. If the sight is to be battery operated, insert the battery and replace the battery cap. If the power converter is to be used, store the battery cap in the case and insert the power converter in the battery housing; rotate it clockwise until it is secure. Connect the cord between the converter and a 115-Vac, 60-Hz power source. The sight is now ready for operation. CAUTION Do not leave the battery in the equip- ment during storage, or corrosive damage may  result. Do  not  remove  the  cover  in  daylight. 2-15