WO2008120153A2

WO2008120153A2 - Aiming of indirect fire weapons

Info

Publication number: WO2008120153A2
Application number: PCT/IB2008/051163
Authority: WO
Inventors: Pieter Francois Smith; Daniel De Villiers
Original assignee: Csir
Priority date: 2007-04-03
Filing date: 2008-03-28
Publication date: 2008-10-09
Also published as: WO2008120153A3

Abstract

An aiming aid (10) includes a support (44), a reflector (24) rotatably mounted to the support (14), the reflector (24) being of a kind which allows optical boresighting of a weapon, and an angular displacement sensor or indicator (36) for measuring an angular displacement of the reflector (24) in use about a vertical axis (32) and relative to the support (44). The invention extends to a method of changing the azimuth of an indirect fire weapon boresighted with an optical sight.

Description

AIMING OF INDIRECT FIRE WEAPONS

THIS INVENTION relates to the aiming of indirect fire weapons or area weapons. In particular, the invention relates to an aiming aid and to a method of changing the azimuth of an indirect fire weapon.

Indirect fire or area weapons such as mortars, have for many years been aimed by using a compass, two aiming poles and a mechanical optical sight. The procedure initially to establish the weapon on a particular bearing or azimuth is however time consuming and not very accurate and it provides limited ability to engage opportunity targets. An improvement to the use of a compass and two aiming poles is provided by the use of an elongate but short (typically 450mm long) prismatic mirror mounted on a tripod a short distance (typically 2m) in front of the weapon. The prismatic mirror allows a user of the weapon to see a reflection of the mechanical optical sight mounted on the weapon, in the prismatic mirror. The reflection can be lined up with an image projected by the sight on the mirror, e.g. a red dot or cross, or with cross-hair or a similar marking of the sight, so that the line of sight of the mechanical optical sight is perpendicular to the lengthwise direction of the reflective surface in the mirror. As will thus be appreciated, by orientating the mirror so that a rear side thereof faces a particular bearing or azimuth, it is easy to line up the weapon to have the same bearing or azimuth (i.e. to boresight the weapon), and by using a mechanical dial on the mechanical optical sight carried by the weapon, it is easy to adjust the azimuth of the weapon to a desired deflection from the azimuth of the mirror. This is simply achieved by dialling the azimuth of the mirror onto a dial of the mechanical optical sight. The optical sight can then be rotated to the desired azimuth, i.e. rotated through the required angle and the optical sight again aligned with its own reflection in the prismatic mirror by turning the weapon carrying the optical sight until alignment of the reflection of the sight in the mirror is achieved (i.e. boresight the weapon). The weapon will then have the desired azimuth.

However, when a large deflection is required from the azimuth of the prismatic mirror, the mechanical optical sight of the weapon, once rotated, cannot be aligned with a reflection thereof in the relatively short prismatic mirror, as the mechanical optical sight, when moved with the weapon and aiming perpendicular to a plane in which the reflective surface of the prismatic mirror is located, is no longer aiming at the prismatic mirror but past it. For practical reasons, taking into account combat conditions, the requirements of portability and robustness, etc, it is not a solution simply to lengthen the prismatic mirror.

It would be an advantage to be able to use an aiming aid which is as simple to use as a conventional prismatic mirror but which allows large bearing changes for a weapon used with the aiming aid. It would also be an advantage to have a method of aiming an indirect fire weapon which employs a reflector, such as a prismatic mirror, but which can handle large bearing changes.

According to one aspect of the invention, there is provided an aiming aid which includes a support; a reflector rotatably mounted to the support, the reflector being of a kind which allows optical boresighting of a weapon; and an angular displacement sensor or indicator for measuring an angular displacement of the reflector in use about a vertical axis and relative to the support.

The reflector may be a mirror operating in the visual light range. Preferably, the reflector is a retroreflector or prismatic mirror, operating in the visual light range. The prismatic mirror may be an elongate prismatic mirror. The prismatic mirror may have a length of between about 300mm and about 500mm, e.g. about 450mm.

The aiming aid may include a protective housing for the reflector. The housing may include a closure member, e.g. a hinged panel or lid that can be opened to expose the reflector, e.g. the prismatic mirror.

The support may be in the form of an adjustable tripod which may be operable to set the reflector level, and/or at a desired elevation. The reflector may be mounted to the support such that an angle between the horizontal and a direction or plane in which the reflector faces, is adjustable. In this way, the reflector can be adjusted to face upwardly or downwardly at a weapon sight, at an acute angle to the horizontal. As will however be appreciated, with a retroreflector or prismatic mirror it is not essential that the mirror faces exactly at the weapon sight, since the retroreflector or prismatic mirror can reflect incident light back in a parallel path where the incident light hits the retroreflector or prismatic mirror over a range of non-perpendicular angles. The aiming aid may include a tilt sensor, e.g. a bubble level. In one embodiment of the invention, the aiming aid includes spaced bubble levels on the protective housing, enabling the reflector to be set horizontal, i.e. with a longitudinal axis of the reflector being horizontal.

The angular displacement sensor or indicator may include or may be in the form of a mechanical indicator comprising a stationary or fixed component or indicator associated with the support and a rotatable component associated with the reflector to rotate with the reflector, thereby to indicate the angle through which the reflector is rotated and/or the azimuth or bearing in which a rear side of the reflector is facing. In one embodiment of the invention, the angular displacement sensor or indicator comprises a pair of circular rotatable dials or rings arranged one above the other and each having a calibrated azimuth scale, and a stationary pointer or marker provided by said stationery component. The dials may be calibrated in mils (6400 mils = 360° and 0 mils usually being used to indicate true north) and one or both of the dials may be angularly adjustable relative to the reflector (e.g. being in the form of a slipring), in addition to being rotatable in unison with the reflector. Typically, one of the azimuth scales is calibrated clockwise and one of the azimuth scales is calibrated counterclockwise, and preferably both dials are angularly adjustable so that they can slip relative to the reflector, without rotating the reflector.

Instead, or in addition, the angular displacement sensor or indicator may include an electronic sensor, e.g. magnetic, optical, induction or resistive sensing capability to measure angular displacement, such as an annular or part annular magnetic strip on one of the stationary and the rotatable component and a magnetic reader on the other of the rotatable and the stationary components, the magnetic reader being positioned to read the magnetic strip, with a signal output operable to provide a signal representative of an angular displacement of the reflector relative to the support, or a bearing of a rear side of the reflector.

The aiming aid may include a compass. The compass may be a magnetic compass, e.g. mounted to the protective housing, or an electronic compass. Instead, the compass may be a Global Positioning System (GPS) compass, operable also to provide the position of the aiming aid, and thus the position of a weapon used with the aiming aid.

The aiming aid may include a sight operable to aim the aiming aid at a distant object. As will be appreciated, by using such a sight, the aiming aid and thus the reflector can be positioned or orientated to face in a particular direction or to have a particular bearing or azimuth, if the direction or bearing of the distant object is known or can be determined. Preferably, the sight of the aiming aid is arranged or operable to aim in a direction perpendicular to a front surface of the reflector or mirror, towards a rear of the reflector or mirror.

According to another aspect of the invention, there is provided a method of changing the azimuth of an indirect fire weapon boresighted with an optical sight on the weapon and a reflector spaced from the optical sight, the method including rotating the optical sight on the weapon to a desired new azimuth or deflection setting, with the optical sight then aiming past the reflector; swivelling the weapon together with said optical sight so that the optical sight is again aiming at the reflector; rotating the reflector about a vertical axis through an angle until the optical sight is aiming in a direction which is roughly coaxial with a bearing or azimuth of the reflector; boresighting the weapon using the optical sight and the reflector; rotating the optical sight through the same angle through which the reflector was rotated, the optical sight being rotated counter-clockwise if the new azimuth is to the right of the reflector and clockwise if the new azimuth is to the left of the reflector; and again swivelling the weapon together with said optical sight so that the optical sight is coaxial with a bearing or azimuth of the reflector, i.e. boresighting the weapon again using the optical sight and the reflector.

In this specification, the term "optical sight" is intended to include sights which project a light beam, e.g. so-called red dot sights.

The reflector may be a mirror operating in the visual light range. Preferably, the reflector is an elongate prismatic mirror. The reflector may form part of an aiming aid as hereinbefore described.

The method may include using a mechanical dial associated with the reflector and having an azimuth scale to measure the angle through which the reflector was rotated. The azimuth scale may be calibrated clockwise or counter-clockwise. Advantageously, using a mechanical dial associated with the reflector may include setting said mechanical dial associated with the reflector and calibrated with an azimuth scale in a particular direction to the desired new azimuth setting of the weapon before rotating the reflector, reading the bearing information on said azimuth scale after the reflector was rotated and then rotating the optical sight of the weapon to the setting of the azimuth scale of the reflector, using an azimuth scale of the optical sight which is calibrated in the same direction as the azimuth scale of the mechanical dial of the reflector. The optical sight will in this way automatically be rotated in the correct direction through the same angle as was the reflector.

Preferably, the mechanical dial associated with the reflector is calibrated in a clockwise direction and the azimuth scale of the optical sight is calibrated in a clockwise direction, for use in a polar coordinate system calibrated clockwise, e.g. in mils.

The method may include setting the dials of the reflector and the optical sight, having azimuth scales calibrated in the same direction, to the actual azimuth of the weapon, once the azimuth of the weapon was changed. In this way, the reflector can act as a reference for new bearing changes or deflections.

Swivelling the weapon together with said optical sight so that the optical sight is again aiming at the reflector, after the optical sight on the weapon was rotated to the desired new azimuth or deflection setting, may include aiming the optical sight at an end of the reflector furthest from the optical sight. The invention will now be described, by way of example only, with reference to the accompanying diagrammatic drawings in which

Figure 1 shows a front elevational view of an aiming aid in accordance with the invention; and Figures 2 to 5 show stepwise the use of an optical sight and the aiming aid of

Figure 1 in a method in accordance with the invention for changing the azimuth of an indirect fire weapon in the form of a mortar.

Referring to Figure 1 of the drawings, reference numeral 10 generally indicates an aiming aid in accordance with the invention. The aiming aid 10 includes, broadly, a reflector assembly 12 rotatably mounted to a support in the form of an adjustable tripod 14.

The tripod 14 is a conventional tripod having three legs 16 that are individually adjustable in length in telescopic fashion. Each leg 16 comprises an outer tube 18 and an inner tube (not shown), with a foot 18 attached to the inner tube. A lock mechanism 20 is provided on each foot 18 to lock the inner tube and the outer tube 18 at a desired telescopic setting. As will be appreciated, by means of the adjustable legs

16 the height of the reflector assembly 12 can be set and the reflector assembly 12 can also be set level.

The reflector assembly 12 comprises a 450mm long prismatic mirror 24 located in a strong protective housing 26 which includes a hinged closure member 28.

In the embodiment of the aiming aid shown in Figure 1 of the drawings, the hinged closure member 28 is hingedly attached to a lower edge of the housing 26 so that it hangs downwardly when in an open condition. Clasps 29 are provided on top of the housing 26 to engage catches 29.1 on the closure member 28 when the closure member 28 is in a closed condition. It is however expected that in a preferred embodiment of the invention, the hinged closure member 28 will be hingedly attached to an upper edge of the housing 26 so that it opens upwardly.

The aiming aid 10 includes two spaced bubble levels 30 mounted on top of the protective housing 26. By means of the bubble levels 30, the protective housing 26, and thus the prismatic mirror 24, can be set horizontal in a lengthwise direction.

The reflector assembly 12 is mounted to the tripod 14 such that the reflector assembly 12 can be rotated about an axis 32 (which is vertical when the housing 26 is set horizontal) and can also tilt about an axis 34 (the axis 34 being horizontal when the housing 26 is set horizontal). In other words, by means of the tilting of the housing 26 about the axis 34, the prismatic mirror 24 can be adjusted to face upwardly or downwardly at a weapon sight, at an acute angle to the horizontal. By rotating the reflector assembly 12 about the axis 32, the prismatic mirror 24 can be set to face in a particular bearing, or more accurately stated, can be set so that a rear surface thereof faces in a particular bearing with a reflective front surface thereof facing in an opposite direction.

Although not shown in Figure 1 , the aiming aid 10 may include a Global

Positioning System compass typically comprising two GPS receivers located at opposite ends of the protective housing 26. The aiming aid 10 may also include an optical sight arranged or fixed at a right angle to the reflective front surface of the mirror 24, by means of which the reflector assembly 12 can be aimed at a distant object so that the rear surface of the prismatic mirror 24 faces towards that distant object.

The aiming aid 10 includes an angular displacement sensor or indicator 36 located between the reflector assembly 12 and the tripod 14. The indicator 36 is operable to measure an angular displacement of the reflector assembly 12 about the axis 32, relative to the stationary support and thus relative to earth.

In Figure 1 of the drawings, the angular displacement indicator 36 is also shown enlarged for clarity. The indicator 36 comprises a stationary disc 38 carrying a stationary pointer or marker 40. The disc 38 is thus fixedly attached to the tripod 14.

Above and below the disc 38, two dials 42, 44 are located. Both of the dials 42, 44 rotate in unison with the reflector assembly 12 about the axis 32. Both of the dials 42,

44 are however also adjustable so that they can be rotated about the axis 32 without the reflector assembly 12 being rotated about the axis 32, i.e. they can be slipped.

The dial 42 is calibrated in mils in a clockwise direction as indicated by the arrow 46. Typically, the dial 42 has a white or silver background with the mils calibration being in black.

The dial 44 is calibrated in mils in a counter-clockwise direction as indicated by the arrow 48. Typically, the dial 44 has a black background with the mils calibration being in white. The dials 42, 44 can be used to indicate the bearing of the reflector assembly 12 and to measure an angular deflection of the reflector assembly 12 from a particular bearing. Thus, if the bearing of the reflector assembly 12 is known, the dials 42, 44 can be adjusted or slipped so that the correct bearing is shown on the dials 42, 44, at the position corresponding with the marker 40. If the reflector assembly 12 is rotated about the axis 32, the actual bearing of the reflector assembly 12 will be shown on the dial 44, in mils. A number of methods is available to orientate the reflector assembly 12 initially and thus to establish its bearing. A first option is to obtain a compass bearing to a distant object and then aim the reflector assembly 12 at this object. A more accurate option is to use a compass mounted on or in the protective housing 26. This compass may be a magnetic compass or an electronic compass. A further, even more accurate option is to use a GPS compass attached to the reflector assembly 12. As will be appreciated, such a GPS compass can also provide the position of the aiming aid 10, and thus the position of an indirect fire weapon, such as a mortar, being used with the aiming aid 10. Yet a further, even more accurate option is to use an electronic map to get the bearing to a very far object, such as a mountain peak, and to aim the reflector assembly 12 at this very far object.

The aiming aid 10 can be used with an indirect fire weapon, such as a mortar 50 (see Figures 2 to 5) to aim the mortar 50 initially and thereafter, if necessary to effect small, but also large, changes to the azimuth of a barrel 51 of the mortar 50.

The procedure to effect large azimuth changes will now be described with reference to

Figures 2 to 5. However, it is first necessary to provide some information, without going into a large amount of detail, of a typical optical sight 52 mounted to a traversing arm of a bipod 54 of the mortar 50. The optical sight 52 typically has a rotatable sight assembly or telescopic sight 56 through which aim can be taken. The telescopic sight 56 may include in its optics a cross-hair or a similar marking, such as a triangle, or the optical sight 52 may be a so-called red dot sight which projects a beam of light producing a visible reflection from a reflective surface (such as the prismatic mirror 24) located in front of the optical sight 52 and visible through the telescopic sight 56.

The optical sight 52 has at least one dial calibrated with an azimuth scale in a clockwise direction. Typically, the azimuth scale is calibrated in mils and the dial is also angularly adjustable so that it can rotate independently of the telescopic sight 56 and also in unison with the telescopic sight 56. Preferably however, the optical sight 52 includes two mechanical dials 58, 60 (shown enlarged in Figures 2 to 5) each with an azimuth scale, the dial 58 being calibrated in a clockwise direction and the dial 60 being calibrated in a counter-clockwise direction, and only the mechanical dial 58 being adjustable so that it can be angularly adjusted independent of the telescopic sight 56.

Typically, the dial 58 has a white or silver background and the azimuth scale is calibrated clockwise in black as indicated by the arrow 70, and the mechanical dial 60 has a black background and the azimuth scale is indicated in white in a counter- clockwise direction, as indicated by the arrow 72.

As is well-known to those skilled in the art, the optical sight 52 usually also has an elevation scale, bubble levels and an azimuth adjustment knob which, when turned through one full turn, will usually rotate the telescopic sight 56 through 100 mils. Usually, the optical sight 52 also has a release button, knob or plunger which can be activated so that the telescopic sight 56 can be rotated freely through large angles so that it is not necessary to turn the azimuth knob to rotate the telescopic sight 56 through large angles.

In order to aim the mortar 50, it is necessary first to boresight the mortar

50 using the aiming aid 10 and the optical sight 52. Firstly, the reflector assembly 12 is orientated so that a rear side of the prismatic mirror 24 faces in a particular direction or known bearing, e.g. using one of the methods hereinbefore described. This known bearing can then be set on a dial with a counter-clockwise azimuth scale, i.e. the black dial 44. Thus, the black dial 44 indicates the true bearing of the reflector assembly 12.

The mortar 50 with its optical sight 52 is typically located about 2m from the aiming aid 10. The optical sight 52 is zeroed so that the optical sight 52 and the barrel of the mortar 50 are aiming in the same direction, i.e. along two parallel but slightly spaced lines 62, 63. Thereafter, the telescopic sight 56 is used to boresight the mortar 50, so that the barrel 51 of the mortar 50 is aiming in the same direction as the reflector assembly 12. This is done in conventional fashion by lining the telescopic sight 56 up with its own reflection in the prismatic mirror 24. This entails adjusting the position of the optical sight 52, and thus the position of the mortar barrel 51 , firstly, if necessary, by moving the bipod 54 and then by adjusting the traversing arm of the bipod 54. When the reflection of the telescopic sight 56 is in line with a cross-hair or a similar marking of the telescopic sight 56, or in line with an image projected by the sight on the mirror, e.g. a red dot or cross, the line of sight 62 of the telescopic sight 56 is perpendicular to a reflective front surface of the prismatic mirror 24. Thus, the telescopic sight 56 is aiming in the same direction as the rear surface of the prismatic mirror 24 and the barrel 51 of the mortar 50 is also aiming in said direction, i.e. the barrel is boresighted.

Once the mortar 50 has been boresighted, the azimuth value, from the black dial 44 of the aiming aid 10 is also set on the white dial 42 of the aiming aid 10 and on the white dial 58 of the optical sight 52. The prismatic mirror 24 now provides a reference bearing for the optical sight 52 and the aiming aid 10 can thus be used as a reference in case the mortar 50 moves due to firing. This initial set up position is illustrated in Figure 2, where the reflector assembly 12 is set with an orientation of due north (0 mils) and with the mortar 50 boresighted so that its barrel 51 also has an azimuth of 0 mils.

In order to illustrate the use of the aiming aid 10 in a method in accordance with the invention to change the azimuth of an indirect fire weapon, it will be assumed that firing instructions are received for the mortar 50 to fire at an azimuth of 942 mils. As illustrated in Figure 3, the telescopic sight 56 is rotated together with the dials 58, 60 so that the new azimuth of 942 mils is shown on the white dial 58. The telescopic sight 56 is thus rotated counter-clockwise through an angle β which is 942 mils. As will be appreciated, for such a large bearing change, the telescopic sight 56 cannot be aligned with a reflection thereof in the prismatic mirror 24, as the telescopic sight 56 is now aiming way to the left of the prismatic mirror 24. This problem is addressed by rotating or swivelling the mortar 50 clockwise as shown in Figure 3 until the telescopic sight 56 is aiming at an end of the prismatic mirror 24 furthest from the mortar 50, as indicated by the line of sight 62 in Figure 3. The white dial 42 of the aiming aid 10 is then adjusted or slipped (without rotating the reflector assembly 12) to read the same value as the white dial 58 of the optical sight 52, i.e. 942 mills, as shown in Figure 3. This is achieved by rotating the white dial 42 in a clockwise direction.

Thereafter, the reflector assembly 12 is rotated counter-clockwise about its axis 32, which should be vertical, until the telescopic sight 56 is aiming in a direction which is roughly co-axial with the bearing or azimuth of the rear surface of the prismatic mirror 24, to allow boresighting. The mortar 50 is then again boresighted using the optical sight 52 and the aiming aid 10, as hereinbefore described, so that the line of sight 62 (see Figure 4) is perpendicular to a front surface of the prismatic mirror 24. Boresighting the mortar 50 may involve slightly rotating the reflector assembly 12 about its axis 32 and/or adjusting the position of the optical sight 52 and thus the barrel 51 of the mortar 50, using the traversing arm of the bipod 54, until alignment is achieved.

As will be appreciated, during this process, the reflector assembly 12 has been rotated through an angle α which, for purposes of this illustration is taken to be 443 mils. As shown in Figure 4 of the drawings, the white dial 42 of the aiming aid 10, being calibrated in a clockwise direction, will now show a reading of 1 ,385 mils and the black dial 44 will show a reading of 5,957 mils, i.e. both dials have been rotated through 443 mils from their starting positions.

Still referring to Figure 4, the telescopic sight 56 of the optical sight 52 is then rotated together with the dials 58, 60 so that the white dial 58 of the optical sight 52 shows the same reading as the white dial 42 of the aiming aid 10, i.e. 1 ,385 mils. This implies that the telescopic sight 56 has been rotated further through the angle α which is 443 mils. At this stage, the black dial 60 of the optical sight 52, being calibrated in a counter-clockwise direction, will show a reading of 5,015 mils.

Lastly, the mortar barrel 51 is then swivelled further clockwise as shown in

Figure 5 and boresighted as set out hereinbefore, so that the line of sight 62 shown in Figure 5 is again perpendicular to the front surface of the prismatic mirror 24. The barrel 51 of the mortar 50 will now have an azimuth of 942 mils. In order to use the aiming aid 10 as a reference on this bearing of 942 mils, the white dial 42 of the aiming aid 10 and the white dial 58 of the optical sight 52 must then be adjusted or slipped to read 942 mils. The optical sight 52 and the aiming aid 10 can then be used to effect changes required in the line of fire 63 of the mortar 50.

The procedure illustrated in Figures 2 to 5 also works for a large azimuth setting for the mortar 50 to the left of the aiming aid 10, i.e. a counter-clockwise swivelling of the barrel 51 . In such a case, the telescopic sight 56 will be aimed at a right-hand end of the prismatic mirror 24 when the barrel 51 is first swivelled. The rotation of the reflector assembly 12 will result in a smaller bearing being shown on the dial 42 than on the dial 58, meaning that the angle α will be deducted from the azimuth setting of the telescopic sight 56 to reduce the angle which the barrel 51 has to form to the new bearing of the rotated prismatic mirror 24, where said angle is measured in a clockwise direction from the barrel 51 to the new bearing of the prismatic mirror 24.

Advantageously, the aiming aid 10, as illustrated, can be used with existing optical mortar sights with no modifications required to the existing mortar sights. The aiming aid 10 and the method of the invention allow faster set up of indirect fire weapons such as mortars and they improve the reaction speed to opportunity targets. The aiming aid 10 can provide a reference for an optical sight and at the same time can be used to get a target or correction bearing. The aiming aid 10 and the method of the invention, as illustrated, provide for a much bigger arc of fire. The aiming aid 10 and the method of the invention can be used with a mechanical optical sight providing no thermal image, which would give away the position of the sight to an enemy.

Claims

CLAIMS:

1 . An aiming aid which includes a support; a reflector rotatably mounted to the support, the reflector being of a kind which allows optical boresighting of a weapon; and an angular displacement sensor or indicator for measuring an angular displacement of the reflector in use about a vertical axis and relative to the support.

2. The aiming aid as claimed in claim 1 , in which the angular displacement sensor or indicator includes or is in the form of a mechanical indicator comprising a stationary or fixed component or indicator associated with the support and a rotatable component associated with the reflector to rotate with the reflector, thereby to indicate the angle through which the reflector is rotated and/or the azimuth or bearing in which a rear side of the reflector is facing.

3. The aiming aid as claimed in claim 2, in which the angular displacement sensor or indicator comprises said stationary or fixed component providing a pointer or marker and a pair of circular dials rotatable relative to the support together with the reflector and arranged one above the other and each having a calibrated azimuth scale.

4. The aiming aid as claimed in claim 3, in which one of the azimuth scales is calibrated clockwise and one of the azimuth scales is calibrated counter-clockwise, and in which both dials are angularly adjustable without rotating the reflector.

5. The aiming aid as claimed in claim 1 , in which the angular displacement sensor or indicator includes an electronic sensor to measure angular displacement, and a signal output operable to provide a signal representative of an angular displacement of the reflector relative to the support, or a bearing of a rear side of the reflector.

6. The aiming aid as claimed in any of the preceding claims, which includes a compass.

7. The aiming aid as claimed in any of the preceding claims, which includes a sight operable to aim the aiming aid at a distant object.

8. A method of changing the azimuth of an indirect fire weapon boresighted with an optical sight on the weapon and a reflector spaced from the optical sight, the method including rotating the optical sight on the weapon to a desired new azimuth or deflection setting, with the optical sight then aiming past the reflector; swivelling the weapon together with said optical sight so that the optical sight is again aiming at the reflector; rotating the reflector about a vertical axis through an angle until the optical sight is aiming in a direction which is roughly coaxial with a bearing or azimuth of the reflector; boresighting the weapon using the optical sight and the reflector; rotating the optical sight through the same angle through which the reflector was rotated, the optical sight being rotated counter-clockwise if the new azimuth is to the right of the reflector and clockwise if the new azimuth is to the left of the reflector; and again swivelling the weapon together with said optical sight so that the optical sight is coaxial with a bearing or azimuth of the reflector, i.e. boresighting the weapon again using the optical sight and the reflector.

9. The method as claimed in claim 8, which includes using a mechanical dial associated with the reflector and having an azimuth scale to measure the angle through which the reflector was rotated.

10. The method as claimed in claim 9, in which using a mechanical dial associated with the reflector includes setting said mechanical dial associated with the reflector and calibrated with an azimuth scale in a particular direction to the desired new azimuth setting of the weapon before rotating the reflector, reading the bearing information on said azimuth scale after the reflector was rotated and then rotating the optical sight of the weapon to the setting of the azimuth scale of the reflector, using an azimuth scale of the optical sight which is calibrated in the same direction as the azimuth scale of the mechanical dial of the reflector.

1 1 . The method as claimed in claim 9 or claim 10, which includes setting the dials of the reflector and the optical sight, having azimuth scales calibrated in the same direction to the actual azimuth of the weapon, once the azimuth of the weapon was changed.

12. The method as claimed in any of claims 8 to 1 1 inclusive, in which swivelling the weapon together with said optical sight so that the optical sight is again aiming at the reflector, after the optical sight on the weapon was rotated to the desired new azimuth or deflection setting, includes aiming the optical sight at an end of the reflector furthest from the optical sight.

13. The method as claimed in any of claims 8 to 12 inclusive, in which the reflector forms part of an aiming aid as claimed in any of claims 1 to 7 inclusive.