1488828 Fire control system DEFENCE SECRETARY OF STATE FOR D S RITCHIE and J G HAMILTON 25 Sept 1975 [9 Oct 1974 16 Nov 1974] 43668/74 and 49816/74 Heading F3C A fire control system for a gun has target position-determining means 10, Fig. 1, a computer 14 which receives signals representative of ballistic parameters and receives signals representative of target position, the computer 14 computing fire control signals therefrom, and has a gun drive mechanism 16 coupled to receive the fire control signals, the target positiondetermining means 10 including a sighting device 11 having a visual display on which first, second and third images are presented in super-imposition, the first image being formed from radiation in the visible spectrum emanating from a field of view, the second image being defined by a target aiming mark, and the third image being formed from radiation in the infrared spectrum emanating from said field of view, the target position-determining means 10 having a manually-controllable element for altering the field of view. In an embodiment a target 13 is surveyed by a rangefinder 12, sensors 15 supply signals representative of environmental parameters to the computer 14 along with signals representative of ballistic parameters and the computer computes fire control signals and applies these signals to the gun drive mechanism 16. The sighting device 11, having the visual display, is observed by an operator at a station 20 having a manually controllable element 21 for altering the field of view of the sighting device 11. The means 10 is coupled by a link 22 to the computer 14 in order to provide signals representative of target position. The rangefinder 12 incorporates a laser 30, Fig. 2, the output beam of which is reflected by elements 31, 32 and 33 to be transmitted through space towards a target located in the field of view of the element 33 which is a plane mirror pivotable about a transverse axis 34 and rotatable in azimuth about an axis 35. Reflected laser radiation is directed by the elements 33, 32 to a beamsplitter 36 which directs the reflected laser radiation to a detector 37 which is coupled to calculating circuit (not shown) to determine the range of the target. Radiation of visible wavelength emanating from the field of view is reflected by the mirror 33 through the element 32 to form part of a visual display for an operator. The display is presented at eyepieces 40, 41 which biocularly present the image of the field of view emanating from the mirror 32 in superimposition with the image of a graticule 42 after having been relayed through elements 43, 44, 45, 46 and 47, the elements 43, 45, 46 and 47 are prism reflectors and element 44 is an image rotation element for correcting the image rotation caused by azimuth rotation of the mirror 33. An IR-reflective mirror 50 obtains an image of the field of view derived from the infra-red indication emanating therefrom. The mirror 50 is coupled to the mirror 33 and a radiation scanning device 51 is provided. The output of the latter is fed to a visible image generating device 52 which superimposes an image on the other two images, the device 52 may be a cathode-ray tube. An image intensifier 53 may be provided along with a prism 43<SP>1</SP>. The aiming mark, obtained from the graticule 42, is in the shape of a circle or an ellipse and a bore sight mark, obtained from the device 52, is in the shape of a triangle. The composite image of the visual display may be relayed to a second monitoring station (not shown) by replacing the element 46 with a prism beamsplitter 46<SP>1</SP>, the composite image being viewed by a camera tube 54 of a television system. Alternatively, a composite image may be formed at a second monitoring station 10<SP>1</SP>, Fig. 6, by providing each monitoring station 10, 10<SP>1</SP> with an optical sighting device 11<SP>1</SP>, incorporating means for generating an aiming mark by feeding signals from the computer 14 to the stations 10, 10<SP>1</SP> to locate the generated aiming marks with respect to the images created by visual radiation within the respective sighting devices, and by generating a visual image from the infra-red radiation received by the scanning device, 51, Fig. 2, and injecting that visual image into each station 10, 10<SP>1</SP>. The sighting device 11, Fig. 3, is driven from the gun drive mechanism 16 through connection 64. The firing ability is restricted because the field of view containing gun bore sight mark 62A, Fig. 3A, requires to encompass the target at all times if the target to be fired at is to remain visible on the visual display 63. The computer 14, Fig. 3, produces fire control signals to actuate the mechanism 16 through an autolay device 60 and simultaneously the aiming mark 62 in the visual display 63 is displaced by corresponding signals to become offset in azimuth and in elevation from the mark 62A. The aiming mark 62 is controlled in dimension by the computer 14 as a function of the target range determined by the laser rangefinder 12, Fig. 1. The sighting device 11, Figs. 4, 4A, has a visual display 63 having an aiming mark 62 which remains centred in the display but is controlled in dimension by the computer 14 in accordance with target range. The gun drive mechanism 16 is coupled to drive the gun and the sighting device 11 and additionally the computer 14 actuates the autolay device 60 and, in the opposite sense, a ballistic drive 70 to cause the gun to be rotated in azimuth and in elevation in relation to the computer fire control signals. The gun drive mechanism 16, Fig. 5, is independent of the sighting device drive mechanism 68 and both utilize a gyro reference signal. The computer 14 is coupled to both mechanisms 16 and 68 and the gun is driven in azimuth and in elevation in relation to the computed fire control signals. In another embodiment an aiming mark generator 90, Fig. 7, is mounted in a gun turret forming part of a first monitoring station having a first sighting mirror 91, a beam splitter 92 and an eyepiece system 93. In addition to the combined image received by the system 93 the beamsplitter provides a combined image which is incident upon a reflector 94. The monitoring station is rotatable independently of the gun, has a sighting mirror 95, an objective lens 96 and an eyepiece system 97. When the station is in nominal alignment with the gun the line of sight between the mirror 95 and the lens 96 is intercepted by the reflector 94 and, consequently, the view in the system 97 is the same as that in the system 93.