' CONFIDENTIAL FOR OFFICIAL USE ONLY NOTES ON ANTI-AIRCRAFT GUNS Compiled at the Army War College From the Latest Available Information APRIL, 1917 WASHINGTON GOVERNMENT PRINTING OFFICE 1917 WAR DEPARTMENT. DOCUMENT No. 5 7"). Office of The Adjutant General, WAR DEPARTMENT, WASHINGTON, April 28, 1917. The following Notes on Anti-Aircraft Guns are published for the information of all concerned. [2582933 A A. G. O.] BY ORDEK OF THE SECRETARY OF AV.\K : H. L. SCOTT, Major General, Chief of Xtaff. OFFICIAL : H. P. MCCAIN, The Adjutant General. 3 ITALY. The Italians use the 75 mm. (3-inch) Deport gun for anti- aircraft service. It has a maximum elevation of 85, and fires 21 shots a minute. Shrapnel is considered inefficient; the high explosive shells, which are much preferred, carry either a time or a detonating fuse. The incendiary shell, used with a time fuse, throws out, upon exploding, a number of small halls con- taining a very efficient burning liquid. Six-gun batteries have been substituted for the formerly adopted two-gun battery. The Italian Army in September, 1916, had 16 batteries (4 guns to a battery) of anti-aircraft guns mounted on automo- biles. The gun, made by Ansaldo & Co., is of 102 mm. caliber. It is reported that the number of these guns has since been in- creased. Illustration No. 1 shows an Italian flat car armed with two anti-aircraft guns. The three heavy brackets (B) are used to brace the car against recoil when the guns are fired. Before firing they are swung out at right angles to the car on the side away from the gun direction and a heavy, threaded, steel rod is screwed down through the band (a) until its lower end presses firmly against a truncated pyramidal block (b), which is placed on the ground to receive it. To facilitate rapid ad- justment a detachable wheel (c) is attached to the top of the screw rod. It is believed that these braces are used only in the case of firing the heavier (6-inch) guns. FRANCE. The main reliance of the French for defense against aircraft is their 75 mm. gun, model of 1897, which fires 25 shots a minute and has a recoil mechanism so perfect that it can be fired con- tinuously without relaying. This gun is shown in illustrations 2, 3, 4, and 5, but the reports show that the mountings have been modified. For anti-aircraft work this gun has been mounted in three different ways, as follows : 5 6 NOTES ON ANTI-AIRCRAFT GUNS. 1. On an improvised fixed mount for the ordinary Hold car- riage. The wheels of the carriage rest on a circular plat Turin with a strong vertical pivot in the center. To obtain the high elevation necessary, the trail is sunk in a circular pit 32 inches below the level of the wheels. In order that the trail may not be driven into the ground, there is attached to it a chock, fitted with a traversing roller resting in the pit on a wooden travers- ing circle. To the pivot supporting the carriage is fixed a pivot collar which turns freely and carries four arms. To each of the two longitudinal arms is attached a tie-rod bolted at the other No. 2. FRENCH 75 MM. FIELD GUN ON FIXED MOUNTING FOR AERIAL DEFENSE OF PARIS. end to the trail chock. These lie-rods resist the recoil of the carriage. To each of the two lateral arms is attached an elastic tie-rod fitted at the upper end with a bronze strap holding the axle of the carriage. The elastic tie-rods are equipped with spiral springs which steady the carriage. A pointing mechan- ism attached to the left-hand side of the trail includes a trav- ersing wheel which actuates, by means of transmitting gears. the traversing chock roller. The field of fire is 360. 2. On a metallic demountable platform for the fixed defense of towns or with a modified substructure for use in the field. In the first case a concrete pit is prepared I meters in diameter and 1 meter deep. At the center of the pit is bolted a base plate with a socket in which turns the vertical pivot supporting the mounting. NOTES ON ANTI-AIRCKAFT GUNS. 7 The framework of this mounting is composed of two trian- gular trusses of riveted U beams iu vertical planes, making an angle with each other of 30 and of two central brackets. To support the personnel, there rests on the trusses and the central brackets a flooring which is open between the brackets to pro- vide space for the trail of the piece and for the winch used for pointing in elevation. The uprights of the two trusses are suitably cross braced, the lower brace being fixed to the pivot No. 3. IMPROVISED ANTI-AIRCRAFT MOUNT FOR FRENCH 75 MM. FIELD GUN. support. At the top these uprights are fitted with trunnion beds designed to receive the axle of the gun carriage from which the wheels, wheel brakes, and shields have been removed. The trail of the carriage is supported by a steel cable wound on the winch, which is operated by means of an elevating mechan- ism on the left-hand platform. To facilitate the elevation and depression of the gun the car- riage has a counterweight consisting of a cast-iron ball placed under the gun and supported from the axle of the carriage by a steel wire cable passing through a hole in the ball and held out 8 NOTES ON ANTI-AIRCRAFT GUNS. by means of a wooden outrigger, one end of which is placed in a recess of the counterweight while the other end is secured to the trail. Each truss is fitted at the rear and under the flooring with a large cast-iron traversing roller, which travels on an iron traversing circle set in the exterior coping of the pit. By turn- ing a handwheel connected to the right-hand roller, the entire framework can be made to rotate around the pivot. Pointing in direction and pointing in elevation are distinct oper- ations, done by separate men. For large movements in direction the mounting is pushed around by hand. The smaller move- ments are given by the before-mentioned traversing handwheel. The cannoneer pointing for direction is on a seat attached to the right-hand truss. In front of him, near the traversing handwheel on a sight bracket placed at the top of a column fastened to the truss, is the sight for direction, consisting of an ordinary telescopic sight provided with a deflection scale. The section commander computes the deflection from the travel of the target during the time of flight, drift, and wind. The can- noneer operating the sight is given the deflection, sets it off, traverses the carriage until the vertical cross hair is on the target, and then keeps the sight on the target. Pointing in elevation is effected either by means of the hand- wheel operating the winch which revolves the entire carriage around its axle or by means of the elevating handwheel of the carriage which turns the gun on its cradle. Both handwheols are within reach of the cannoneer pointing for elevation, who stands on the left-hand platform. Elevations from 12 to 85 can be obtained. The sight for elevation is an ordinary telescopic sight, the mounting of which is in gear with the range dial. The can- noneer at this siglit keeps the horizontal wire of his sight on the target at all times by elevating or depressing the gun by means of the elevating handwheels. The range dial, about a foot to the left, is operated by another cannoneer. It consists of a small brass- disk on which are curves corresponding to the different ranges. By moving the pointer along these curves to the range given, the necessary elevation is transmitted to the telescopic sight for elevation. Thus, when a change of range is announced, the gunner being already on the target, the can- noneer moves the pointer to the new range: this throws the gunner off the target, and he at once relays the piece. NOTES ON ANTI-AIRCRAFT GUNS. 9 The detachment consists of a chief of section and eight can- noneers viz, a pointer in elevation, a pointer in direction, a firer, a loader, a fuse setter, and three ammunition carriers. For use in the field the substructure of this platform mount is simplified. The shape of the pit is that of a truncated cone ; it is dug 1 meter deep, 1.8 meters in diameter at the bottom, and 4 meters in diameter at the top. A small parapet about 2 meters thick around the rim is formed of the excavated earth. The pivot socket is bolted to a bolster consisting of two layers No. 4. ANTI-AIRCRAFT GUN ON AUTOMOBILE. of wooden joists bolted together, and is centered in the traverse circle by 8 iron tie rods. The iron traverse circle is bolted to 12 blocks of wood. For transportation it is taken down in four parts, which can be carried in two wagons. In mounting and dismounting the gun and carriage an as- sembling shears is used. The time taken is as follows : To dig ditch, 1 hours ; to mount platform, \ hour ; to mount gun, 5 minutes ; to dismount the whole, 35 minutes. 3. On an automobile. To prepare for action the chassis is supported by four jack screws. In addition two side supports are lowered to the ground, to prevent overturning. The car- riage permits angles of elevation from to 70. The hori- 96836 17 2 10 NOTES ON ANTI-AIRCRAFT GUNS. y.ontal lit-ld of lire is limited to 240, as the breach can not pass certain positions. Until recently time shrapnel was used almost exclusively, but now the French are using high-explosive shells with time fuses. When shrapnel is used the entire percussion element is removed, for the protection of friendly troops, in case the time element of the fuse does not function. There is also a smoke-producing shell, filled with fuse composition, and the ogive is pierced with holes. It is primed with a time fuse, which communicates No. 5 FRENCH OFFICIAL PHOTOGRAPH FROM THE SOMME. flames to the interior charge, which escapes through the holes in the ogive. Thus it is possible to follow the projectile through its trajectory, which is of great assistance in anti-aircraft gun- nery. In addition to the 75 mm. gun, it is known that the French are using for aerial defense the 105 mm. gun, also the 37 nun. rapid-fire naval gun. In Paris some 37 mm. guns are on tripods, while one is in a cupola. No further information is on hand. According to the latest information received on anti-aircraft guns on automobile mounts, the 75 mm. gun is used for firing a shrapnel weighing 7.4 kilograms (16J pounds) with a muzzle velocity of 525 meters per second (1,722 feet per second) and NOTES ON ANTI-AIRCRAFT GUNS. 11 a high-explosive shell weighing 5.315 kilograms (111 pounds) with a muzzle velocity of 584 meters per second (1,815 feet per second). This fire appearing insufficient against aeroplanes flying at great altitudes there is now under consideration a 90 mm. anti-aircraft gun. with a muzzle velocity of approxi- mately 750 meters per second (2,460 feet per second) for a shrapnel weighing 11 kilograms (24 pounds). The use of the 75 mm. gun with a high muzzle velocity ap- pears to be preferable to that of the 105 mm. with a reduced muzzle velocity. GERMANY. The German have used for anti-aircraft work numerous dif- ferent types of guns, generally ranging in caliber from 50 mm. No. 6. EHRHARDT 65 MM. ANTI-BALLOON GUN L-35. to 105 mm., though calibers as low as 37 mm. and as high as 120 mm. have been reported. Some of these guns had already 12 NOTES ON ANTI-AIRCRAFT GUNS. been developed before the war began, while others have since been brought out, the tendency being toward a constant in- crease in caliber, range, and muzzle velocity. The incomplete and sometimes more or less conflicting reports concerning some of these guns make it difficult to coordinate the data on hand, which for some guns are very meager. The earliest German antiaircraft gun of which we have any information is the 65 mui. (2.56-inch) Ehrhardt anti-balloon gun developed several years before the war. This gun is 35 calibers long, fires with a muzzle velocity of 2,000 feet per sec- No. 7. EHRHARDT 65 MM. ANTI-BALLOON GUN. ond, a 9.4-pound projectile, at a maximum elevation of 75 to a maximum height of 26,000 feet. The maximum range for time fuse is 5,960 yards, and for percussion fuse 7,760 yards. The gun has quick and slow movement in azimuth and all-around fire. It is mounted on a center-pivot cradle carriage on an au- tomobile truck with broad wheels weighing about 7 tons (illus- trations 6, 7, 8, and 9). Weight of gun and carriage is 1,900 pounds. With a level and two handwheels the upper carriage can be quickly leveled. The automobile has a wide gun plat- form with seats for the crew, ammunition chests for 130 rounds, and fuel tanks holding sufficient for 18 hours. In the firing position this platform is widened by dropping hack its sides and is supported off the wheels by iron props resting on a broad metal base. The average speed is 50 kilometers (31 No. S.-EHRHARDT 65 MM. ANTI-BALLOON GUN. No. 9. EHRHARDT 65 MM. ANTI-BALLOON GUN. 13 14 NOTES ON ANTI-AIRCRAFT GUNS. miles) an hour. In order to secure the necessary rapidity of fire, the breech mechanism has been provided with an appa- ratus for automatically opening and closing the wedge-shaped breechblock. A noteworthy feature of the gun is the automatic sight, which is so constructed that it is only necessary to set off the actual range in a straight line to the target whatever its altitude, found by means of a telemeter, and to bring the target on the cross hairs. The line of sight is capable of two movements, one which sets off the necessary angle between the NO. 10. KRUPP 71 MM. L-30 ANTI-BALLOON GUN. axis of the bore and the line of sight when the target is in the horizontal and the other which corrects for the altitude of the target by automatically decreasing this angle to a theoretical zero at the zenith. There is also an automatic fuse time indi- cator. This is a brass plate with curves and a movable arm fixed in the trunnion opposite the sight. It is only necessary to set off the given range and lay the piece on the target, then the proper time can be read. Another anti-aircraft gun developed by the Germans some years before the war is the 71 mm. (2.8-inch) Krupp anti-balloon gun (illustrations 10 and 11), tiring '20 to !!"> shots per minute. NOTES ON ANTI-AIRCRAFT GUNS. 15 This gun is 30 calibers long, fires with a muzzle velocity of 2.130 feet per second an 11-pound shell at a maximum elevation of 75 at a maximum height of 21,300 feet. Traverse, 360. This gun is a barrel-recoil gun on a center-pivot carriage, mounted on an automobile which can also be armored. Weight of auto- mobile without gun, 7,180 pounds ; with gun, about 9,900 pounds ; with armor and ammunition chest (carrying 122 rounds), about in.400 pounds. Mean speed, 28 miles an hour. The gun has an automatic horizontal crank closure, rear trunnions and NO. 11. KRUPP 71 MM. L-30 ANTI-BALLOON GUN. spring compensator, liquid brake, toothed-arc laying apparatus, and traversing apparatus which can be thrown out of gear for rapid movement. It is also known that the Germans had before the war de- veloped a 105 mm. (4.1-inch) anti-aircraft gun on center-pintle mount for fixed emplacements, with full automatic breech mech- anism. Further details, however, are lacking. A small-caliber anti-aircraft gun of high initial velocity was, according to one report, brought out by Krupp during the sum- mer of 1915. This gun has a caliber of 53 mm. (2.09 inches) and a range of between 4,000 and 5,000 meters (13,120 feet and 16,400 feet). The initial range for firing being given the gun sights increase in range automatically 50 meters (164 feet), so 16 NOTES ON ANTI-AIRCRAFT GUNS. that the shells explode in series 50 meters apart. Three guns are usually placed in position together, and a zone of lire is thus established and maintained around the hostile aircraft. Several aeroplanes were brought down during that summer by this .mm. No further data are available. One report made during the summer of 1915 gives some infor- mation about the firing of a 77 mm. (3.03-inch) Krupp semi- automatic gun of about 35 calibers, mounted on a pedestal base upon a motor truck. The range finder, which was mounted on a tripod on the ground near the truck, was between 1J and 2 meters long, and was of coincidence type, with internal and external readings. On the pedestal mount was a level, so that the mount could be leveled before firing. The sight consist .et I of a telescope with two eyepieces, one of low and one of high power, so close together that the eye could change readily from one to the other. In each eyepiece appeared a triangle, point up. The gun pointer brought the aeroplane within the triangle of the lower-power eyepiece, which was used as a finder, and then, shifting his eye to the high-power lens, he brought the aeroplane on the point of the triangle. The gun crew consisted of three men, one man to aim, one to load, and a third to bring the ammunition from the rack and adjust the fuses^ Two officers were also present, one of whom managed the range finder, while the other gave the firing directions. Eighty-one shots at a French aeroplane at ranges increasing from 3,600 to 7,100 meters were witnessed. All shots were fired in groups, first of three and then of six shots. The mounts were clamped during the firing of each group. The interval between shots was 2>. seconds; the interval between groups varied, as each group was allowed to burst before the order to fire the next group was given. The shells burst with a thick white smoke. The powder used in the gun was absolutely smokeless, thus giving no clue to the location of the gun. The aeroplane was not hit. A year later, namely, during the summer of 1916, a few data were received concerning an anti-aircraft coast battery of four 88-millimeter (3.46-inch) guns with semiautomatic breech mechanism on shielded pedestal mounts admitting of a maxi- mum elevation of 75. The guns were located at the corners of a square having a diagonal of about 100 meters. At the center of this square was the battery commander's station with self- contained horizontal base range-finding instrument, telephone connection with' central to receive early notice of approaching NOTES ON ANTI-AIRCRAFT GUNS. 17 hostile aircraft, and megaphone for giving verbal orders to the gun crews. According to a report submitted late in 1916, the Germans were then using four guns for anti-aircraft work, which, in the chronological order of their adoption by the Germany Army, were stated to be : 1. A 50-millimeter (1.96-inch) Ehrhardt gun 30 calibers long, firing a 1.25 kilogram (2.75 pounds) high-explosive shell with a muzzle velocity of 572 meters per second .( 1.877 feet per >e<-- ond). Sometimes a 2.4-kilogram (3.08 pounds) shrapnel shell is used. The maximum elevation is 70. This gun, on a cen- tral pivot gun carriage with cradle, is mounted over the center of gravity of an armored car. The cradle contains a hydraulic brake and a spring recuperator. The sighting apparatus in- cludes a muzzle sight and a mobile breech sight. The gun is pointed by means of a butt against the shoulder of the gunner. For this gun there are two models of motor car, differing only in their armor plating. The heavy model (plate of 7-millimeter nickel steel) can do 48 kilometers (30 miles) an hour on level ground and can climb gradients of 22. The light model (4-mil- limeter nickel steel plate) can exceed 60 kilometers (37 miles) an hour. The latter car has a total weight of 3,200 kilograms (7,057 pounds) when carrying five men and material for 100 shots in the munition case at the back which also serves as a seat. '2. A 65-millimeter (2.56-inch) Krupp gun 35 calibers long, temporarily mounted on a 4-ton motor truck. No further de- tails given. 3. A 75-millimeter (2.95-inch) Krupp gun. 35 calibers long (illustration 12). This gun has a muzzle energy of 110 meter tons, corresponding to a 5.5-kilogram projectile, and an initial velocity of 025 meters. With an elevation of 75 it can attain a maximum height of 6.300 meters (20.670 feet). Since Janu- ary, 1915, it is mounted on a specially constructed motor truck with solid tires front and rear and weighing 3.920 kilograms (8,640 pounds). The motor develops about 75 horsepower and on a good track has developed a speed of 58 kilometers (36 miles) an hour. 4. A 105-millimeter Krupp gun, 35 calibers in length (illus- tration 13). This is the last gun developed. This special 105- millimeter gun fires an 18-kilogram shell with a muzzle velocity of 700 meters per second (2.300 feet per second) and at the maximum elevation of 75 reaches a height of 11,400 meters 18 NOTES ON ANTI-AIRCRAFT GUNS. (37,400 feet). The total weight of the gun is 3 tons (1,400 kilograms for the tube. 1.000 for the pun carriage). The gun was originally constructed for use on a field-L'iin carriage. Inn at the request of the German general staff the Mercedes work- shop succeeded in constructing a motor truck for it which can easily make 40 kilometers (25 miles) an hour on good roads. The tires, solid front and rear, with a diameter of 1 meter, are of cast steel. The car is equipped with a G-cylinder motor NO. 12. KRUPP 75 MM. L-35 FOR AUTOMOBILE MOUNT. developing 160 horsepower. The driver is the only man on board. The ollicer in charge, the chief gunner, and four men follow in an armored car capable of 70 kilometers (43 miles) an hour and carrying munitions, as well as an armament of two machine guns. It is believed that this gun is frequently used on a fixed mount also. A report submitted late in 1010 states that in order to pre- vent hostile aviators from Hying low enough to do effective NOTES ON ANTI-AIRCRAFT GUNS. 19 work with their machine guns, as well as to provide for the close local defense of balloons, aviation parks, etc., the Ger- mans have been installing machine cannon of 37 millimeters (1^-inc'h) caliber. They fire a solid shot with a smoke-tracing compound in the base. The feeding is by strips, 24 cartridges to a strip. Another late report mentions a visit to two German anti- aircraft batteries for the protection of Ostende and Zerbruegge, respectively. Each battery consisted of four 4-inch 50-caliber guns mounted in a square about 100 meters on the side. One late report also gives a few data concerning a 120-milli- meter (4.72-inch) Krupp anti-aircraft coast gun, namely, that NO. 13. KRUPP 105 MM. ON MERCEDES TRUCK. it is 45 calibers in length and fires a 24-kilogram (53-pound) projectile with an initial velocity of 800 meters per second (2,625 feet per second) at a maximum elevation of 60. Illustration 14 shows an unidentified German anti-aii-craft gun. Captured 75-millimeter French field guns in improvised bat- teries are also often used for anti-aircraft work. To secure the high elevation necessary either the wheels are set on a raised center pintle with a circular track or, the wheels remain- ing on the level surface of the ground, a circular trench is excavated for the trail of the gun to move in. 20 NOTES ON ANTI-AIRCRAFT GUNS. No. 14. GERMAN ANTI-AIRCRAFT GUN. The following table, though its data can not in general be brought into relation with those compiled above, is added be- cause very recently received : Type and caliber. Initial veloc- ity. Projec- tile, weight. Maxi- mum eleva- tion. Range. Weight of gun and car- riage. Weight of gun, car- riage, and limber. Muzzle energy. KBITPP. 75 mm. 30 cal. field car- riage. Meters. 510 Kilo- grams. 6.5 65 Meters. Kilo- grams. 1,030 Kilo- grams. Meter- tonx. 71 mm. 30 cal. on auto- 1 5,850 mobile 1 650 5 75 6,500 1,230< 7,100 104 mm. 45 cal. coast gun 800 15.5 60 120 mm. 45 cal. coast gun 800 24 60 EIIRIIARDT. 50 mm 30 cal on auto- / 5 3, 100 mobile 570 1.25 70 3,720 { 2,800 65 mm. 35 cal. on auto- mobile 670 4.1 75 7,900 6,000 93.73 75 mm. 30 cal. on auto- mobile . . . 500 6.5 70 5,860 6,300 82.76 105 mm. 32 cal 605 17 70 8 300 ( 6,50 75 mm. 32 cal. field car- riage 550 6 5 70 6,800 1 6 5, 900 1,800 100.10 i Without men and ammunition. With shields. 6 With trailer. > With men and ammunition, Without shields. 5 Without trailer. NOTES ON ANTI-AIRCRAFT GUNS. 21 ENGLAND. Aerial defense in the English Army consists of: (1) Fixed anti-aircraft artillery; (2) mobile anti-aircraft artillery; and (3) aeronautical units (not here under consideration). Various types of anti-aircraft guns are in use. Among them are some 4.7-inch naval guns, some 75 mm. French guns, and some 5-inch breech-loading rifles. The later types in more com- mon use are the 3-inch 13-pounder, the 3.3-inch 18-pounder, and finally the 3-inch 15-pounder, which ultimately is to replace them all. The converted 3-inch 13-pounder is the former horse artillery gun, with breech bored to take a longer cartridge (with an 18-pounder charge) giving an increased muzzle velocity of ;,bout 2,000 foot-seconds. These guns are equipped with the ordinary field artillery hand-operated breech mechanism and are mounted for mobile work on pedestals built up on auto- mobiles and revolving through 360. There is one gun to each motor truck. These motors are of 45 horsepower. Their sides are dropped and their wheels blocked when in use. The maxi- mum range is from 6,700 to 7,000 yards, and the highest eleva- tion is 75. Six batteries of these guns of six guns each are used in the London area. The 18-pounder is the service 18-pounder field gun mounted for anti-aircraft service. These guns also have the hand- operated breech mechanism. They give an initial velocity of about 1,750 foot-seconds. They are mounted on transportable platforms (see below). Some of these guns have been relined and the bore decreased to 3 inches. These relined 18-pounders fire a 13-pound projectile with an increased velocity of approxi- mately 2,000 foot-seconds. Some of these relined 18-pounders are mounted on automobiles. The anti-aircraft guns which are on automobiles are mounted directly over the rear axle of standard 3-ton motor trucks provided with two outriggers, so as to permit of firing across the truck. The rear outrigger consists of a telescoping beam capable of being drawn out about 4 feet beyond the sides of the truck. At its outer ends are two jackscrews which distribute the load over about 3 square feet of ground by bearing upon blocks which are carried on the truck. The front outrigger just behind the driver's seat extends out only sufficiently to permit of the use of the jackscrews. The body of the truck is provided with sideboards 22 NOTES ON ANTI-AIRCRAFT GUNS. which, when dropped down, extend the platform about 20 inches on each side. The trucks have single tires in front and double tires in rear and are equipped with governors limiting the speed to approximately IN miles an hour. They carry a small amount of ammunition, while additional ammunition is carried on other motor trucks. The latest gun, one which has been especially developed dur- ing the war for anti-aircraft work, is the 8- inch 15-pounder 20 hundredweight gun on a pedestal mount. This is the one gun which has been adopted as standard for the service and is to replace all others. It is considered the best gun for the pur- pose and it is reported that both French and Italian officers admit its superiority to any yet developed. It is being supplied to all anti-aircraft stations as rapidly as possible. It was built to have an initial velocity of about '2. 7~>0 foot-seconds, now reduced, however, to 2..">0 foot-seconds, because with a higher velocity the gun wears out too rapidly. The gun is 45 calibers long and has a height range of 2.~>. feet square and IS inches deep. Four arms about 4 feet in length are hinged at the corners so NOTES ON ANTI-AIRCRAFT GUNS. 23 that they can be swung to the firing position on the diagonals of the platform and locked by pins through the platform, which is thus extended sufficiently to give the gun stability. On the bottom of the platform and on each of these arms are angles approximately 3 by 3 inches, which by engaging the surface of the ground prevent lateral movement. At the end of each arm is a jackscrew. To go into action the trailer is detached from the motor car, the arms swung out and locked, and the jack- screws run down until the weight is taken off the two wheels of No. 15. BRITISH ANTI-AIRCRAFT QUNS ON THE WESTERN FRONT. the trailer. As the wheel axle is jointed in the middle and held together by a latch, this latch is now released and the two wheels being then withdrawn, the jackscrews are run out until the platform rests on the ground ready for firing. It takes jx trained crew only about one minute to place the gun in action. The gun crew consists of 11 men. The 15-pounder guns, with some 18-pounders, mounted on trailers are used in anti-aircraft defenses in England (84 of the former are eventually to be provided for the aerial defense of London) for the protection of ammunition stores, bases, etc., and behind the firing line in France. The guns mounted on motor trucks (13-pounders and some 18-pounders) are used im- 24 NOTES ON ANTI-AIRCRAFT GTJNS. mediately behind the front line trenches and also for reinforcing the anti-aircraft fire wherever necessary. No. 16. BRITISH ANTI-AIRCRAFT GUN AT SALONIKI. Illustration 15 shows a British anti-aircraft gun on the west- ern front, and illustration No. 16 one at Salonica. UNITED STATES. The only weapon designed for use by our Army specifically against aircraft is a 3-inch 15-pounder, having the same con- struction and ballistics as the 3-inch 15-pounder model of 1903. This piece will be equipped, however, with a semiautomatic breech mechanism and a drop block. The carriage provides for firing the gun at elevations between and 80. It is antici- pated that a maximum altitude of about 30,000 feet can be obtained with this gun when using a projectile with a 7-caliber ogive and a muzzle velocity of 2,600 feet per second. The Ordnance Department is designing or building three dif- ferent types of mounts for anti-aircraft artillery. The first is a fixed pedestal mount for the 3-inch 15-pounder gun ; the other NOTES ON ANTI-AIRCRAFT GUNS. 25 two mounts are for a 3-inch field gun, model of 1902, one to be emplaced on an automobile truck, the other on a semiportable platform. All mounts will permit a maximum elevation of 85. The minimum elevation of the automobile mount will be 35, while that for the semifixed and 3-inch 15-pounder mounts will be 12 and 0, respectively. It is understood that the Engineer Department has plans for mounting the standard 3-inch antiaircraft gun and carriage as follows : (a) On a standard railway flat car of 80,000 pounds capacity, equipped with outriggers which will enable the gun to be fired from the car at any point by blocking up under the ends of the outriggers. ( I) ) On a light flat car running on light standard gauge, which can be pushed, if necessary, from point to point and which can be quickly anchored to a concrete platform to be constructed in advance and laid flush with the ground under the track at points where it is desired to bring the gun into action, the gun to be fired from the car after it is anchored to the platform. (c) On a truck from which the gun can be fired in the same manner as explained under (b), but which can be hauled over ordinary roads by teams or automobile tractors. The methods outlined above are considered by the Engineer Department to be the cheapest and most practicable for the mobile use of the standard 3-inch anti-aircraft gun and car- riage. By making use of concrete platforms for anchorages which are laid flush with the ground, a practically level base for the gun when fixed is secured and the platform can be concealed by an earth covering when not in use. It is also practicable to make provisions for bolting the gun pedestals directly to the concrete platforms if desired. The new Navy anti-aircraft gun, developed .after three years of experiment, is a machine rifle about 50 calibers long and capable of hurling a 3-inch shell 27,000 feet into the air at an angle of 90, and can deliver its charge at rapid-fire rate. CONCLUSIONS. The aeroplane has been steadily forced to higher altitudes, and to counteract this the anti-aircraft gun has shown a corre- sponding tendency to increase in size, power, and range. The 26 NOTES ON ANTI-AIRCRAFT GUNS. size of aerial defense trims used in the present war has ranged from machine guns to those (if 4. .". and (> indies in caliber. Aircraft are comparatively safe from machine-gun lire at altitudes greater than ,S,.~i