"SPOTTING" FOR THE GUNNERS

Dominion, Volume 11, Issue 253, 13 July 1918, Page 3

"SPOTTING" FOR THE GUNNERS

HOW THE AIRMAN DOES IT

THE EYES OF THE BATTERY

(By a Eoyal Flying Corps Officer.)

[Published by tho War Office, and circuialed/by tho Uoyal Colonial institute.] Artillery observation is one of Hie most important functions of aircraft iu war. Uy means of aerial indication and detection of targets, Runs, especially longrange- guns, have increased enormously in value. Nor is this service confined toland batteries, for 15in. guns of warships have a range beyond- tho horizon visible from thoir fighting tops, and seaplanes can direct their fire (in targets on!; of sight of the gunner. Kite balloons are also employed in "spotting" for the artillery, but they are more vulnerable to enemy aircraft, and possess no means of self-defence, and they cannot compare with tho two-seater aeroplanes, equipped with wireless, which are generally used for this work. Previous to the general adoption of wireless, communication from ueroplanes to bnttorv wns effectod by dropping different coloured lights or smoke-balls, nnd by manoeuvring in the air, such _ as circling to right and left, describing figures of eight, etc.—a limited code which was interpreted on tlio ground with difficulty. These .methods may be still employed when "wireless" breaks , down.

In the case of operations' t-ver "the lines" aernplanes are. usually wiuinned with ai)paratu3 for transmitting nigssagos. In the presence enemy aircraft over the Imtrory's jiosilion. prronnd siftrialling and fire is suspended until the hostile visitor is driven off, so that positions shall not bo located.

All messages are coded, for brevity and secrecy. By the use of different "wave" lengths. 'Several machines can work in 'the same area and at the same timo without "jamming." Special artillery maps of the whole of tho' enemy's country, prepnred from existing maps or aerial photographs, are divided into lettered and numbered squares and subsections; an aeroplane, after indicating ft target by "wirPlefsin?" its position on the maji, observes and directs the fire of tho , guns. Targets once located and ranged are "registered" and generally allotted to whichever particular battery has the most favourable range and is best situated for shelling, although on occasion the whole of the fire of a group of batteries can be brought to bear by a simple general signal understood by all -batteries in range. An experienced artillery spotter' can work several batteries at one time when necessary, switching on and off to fresh targets and other batteries, especially whon over an area well known from previous spotting excursions.

As machines engaged in the work of artillery .observation are not so fast as the small single-seater craft designed for fighting, they are frequently the object of attack from hostile fighters. Nowan friendly fighter is told off to "sit" above tho artillery machine on "patrol," where it is ready to swoop <lown on any enemy machine decoyed by tlio'apparently easj; mark nf the slower 'planes. Airmen who have been artillery officers fire generally employed as "spotters." Their knowledge of time tnken batween rounds, time of flight of shells, otc, for guns of different calibre makes for successful co-operation between the two arms.

The Airman's Qamora. The improvement of aerial photography has kept pace with tho development of other branches of aeronautics; the securing of photographic evidence ol the enemy's defences being an indispensable preliminary to any attack, especially in trench warfare. The aoroplaue camera has evolved from tho apparatus held over the side of tho machine in tho airman's grasp, or strapped round his 'lock, which gave comparatively poor results at tho limited heights to which aeiopliineu ascended at the outbreak of war to the fool-proof, self-winding, and si'ifoxnosiiig devices of tu-day. These enable the airman to map any route on a strip of film with no moro trouble than tlio initial setting, for height aud groundspeed.

Plates being preferable to films (for woll-known reasons which need not bo given here) the majority of nero-cniiicraa in uso to-day aro constructed to receive a magazine of plates, wbich can Ijo recharged in the uir from a stock curried in the photographer's cockpit. Jjoxtyped cameras of fixed focal length aro used. The use of "bellows" cameras would not; ensure the pliUes lying in a parallel piano with tho lei Vs. Some timo ago exposures were generally made from various altitudes, depending on tho subject and nature of anti-aircraft ddences. Un occasions aeroplanes descend within ii few hundred feet of the ground to securo photographs of some purliuniur object, euch as gun emplacements, and special cameras of long focal length are used to produce largo pictures of sectors of the ground. These in turn arc- enlarged and microscopically examined, and the eye of mi expert determine gunpits from such details as ''muzzlo-

blasts" (the scorching of foliage, etc., produced by tho guuj and ammunition cartwheel marks.

The length of exposure is determined by the aeroplane's speed over tho ground.

At the height from which phoiograpiis aro usually taken the apparent million, during a fraction of a sfcond, of tho aeroplane relative to the earth is very slight. The shutter enn be set lo give an exposure of a thousandth part of a second, but this speed is only used for. exposures made from low-flying aeroplanes. It is important for tho airman to note the height at which his photographs are taken, so that maps can bs prepared to scale. Tho ratio of of the negative to that of the ground covered is the same ns that of the camera's focal length to the height at which the exposure was made. Using ain. and 4in. plates, the area- included in an aerial photograph taken at normal heights is about 151)0 yards bv 1200 yards, so that the use of view-finders is necessary, the airman judging when his machine is over the centre of Iho area. Particular care

has to be lakeii to keep the machine level when tnking photographs, otherwise the scale of overlapping prints would not coincide. Cameras fitted with lens of longer focal lenglh nnd (huso used at low aUitudes, however, aro provided with sighting wires. The whole ofitlie maps for the operations around Kut iu Mesopotamia were prepared from aerial photographs. The city of liagdad was mapped by air in i\ fraction of tlio time it would have taken surveyors to traverse the maze of streets in a town of this size.