INDIRECT LAYING SYSTEM IN USE BY BRITISH EXPEDITIONARY FORCE IN FRANCE.

            The site for the Battery and general directions in which fire will be required having been ordered, the line of guns are placed approximately at right angles to this line.

            If covered emplacements are built, it is very important that each dial sight should be able to see the aiming point.

            The gun on one flank is usually chosen as directing gun.  The corrections for the other guns will be simpler if the aiming point is at right angles to the line of fire, but it is very difficult to make a covered emplacement which allows of this.  In the battery I saw, the aiming point was 45^o right of rear.

            The exact position of the directing gun is then marked very accurately on the map, and a line drawn through it for a normal axis of fire.  This is called the zero line.  Also a line on the aiming point – the angle between these two is then measured by the dial sight.

            If the zero line can be laid on a seen object marked on the map, there will be a chance to check accuracy.  The distance between the guns is then carefully measured, and the angle between the aiming point and the zero lines calculated.  This should bring all the zero lines parallel, and pickets on which lamps can be hung are placed to mark them.

            A line is drawn on the map behind the enemy’s position at right angles to the normal axis of fire; and degrees right and left set off along it, as calculated from the directing gun.

            A paper straight edge is pivoted at the directing gun, and when this is brought over the target, the angle right or left of the normal axis of fire can be read off on the scale of degrees.

            A scale of ranges, allowing for the shooting qualities of the cordite in use, is marked on the edge of the paper straight edge, and immediately gives the range of the target from direction gun.  When this is known, the correction in line to concentrate the other guns on target is easily got from a table.

            To get the exact line – only a cross wind need now be allowed for.

            To get the elevation – a headwind, barometer and thermometer corrections must be made.  Also for difference of level of gun and target, if any.

            After the first shot, the forward observing officer signals corrections.

            Aeroplanes directing guns first signify the target by the usual map nomenclature by wireless.

            After the first shot, they signal the angle from north and the distance of the spot where they wish the next shot to fall.

            The Battery Commander has a scale and circular protractor device by which he can readily calculate the necessary corrections in angle and in elevation for his guns.

(Sgd.) P.F. Molony Major.

R.E.

24/2/16.