Field guns adapted for antiaircraft fire

In October 1915 the Bulgarian Army had only two true anti-aircraft guns. In order to assure an adequate protection to the country against air raid, it was necessary to increase the number of the guns available. Since it was impossible to buy them abroad, the Bulgarians adopted the same trick used by all the major powers at the beginning of the war. Field guns stored into the depots or assigned to fortress artillery were put on improvised mountings in order to increase their elevation, and were used in the place of anti-aircraft guns. Since at the beginning of the war Bulgaria had not enough quick-firing guns to arm all the field artillery batteries, at first col. Rakovski had to use the old 87mm Krupp slow-firing guns. The low muzzle velocity of them soon led the request for more effective anti-aircraft guns. The next step was the use of modern field guns. Every kind of field gun used by the Bulgarian Army during the war was in a great or a little number utilised also as anti-aircraft artillery. Like Germany, Bulgaria used also some captured guns : 75mm Schneider Serbian and 75mm Krup Turkish guns.

At the end of the war, among the guns used by the Bulgarian Air Defence only 30% were true anti-aircraft guns, 39% were quick-firing field guns and 31% were old slow-firing guns. The first problem was to adapt guns designed for horizontal fire in order to perform an effective vertical fire. Consequently in order to perform vertical aiming of the regular guns to an angle of 40° - 50°, a pit was dug under the gun trail. Such expedient, so as a lot of improvisation devised by talented artillery officers, were largerly ineffective against aircrafts, but evinced at least a deterrent effect, forcing the enemy planes to gain altitude.

Later col. Rakovski developed a special rotating arrangement which enabled an increased elevation angle. On 21 March 1918 it was submitted to the Head of the artillery, who decided to introduce it into the army. It enabled the Schneider and Krupp field guns to fire with an elevation angle of 60°. On a wooden platform 20/30cm in diameter at 1.50m from the ground, he placed a beam of convenient length, at which both the wheels of the gun carriage were connected through chains, so that, turning the beam around the platform by means of a pivot placed on it, the gun could fire with facility in every direction. In order to fire under the correct angle of elevation, the gun layer was placed in a small ladder attached to the carriage and revolving with it.

The problem of adapting field guns to anti-aircraft fire was faced up by every Army and a lot of ingenious solution were invented (see the pictures).

According История на зенитната артилерия…, p. 24 at the end of the war the Bulgarian Army used guns of four different calibres and six different patterns:

- 87mm Krupp old pattern field guns,

- 77mm Krupp field guns, supplied by the German Army,

- 76.2mm Putilov anti-aircraft guns, captured from the Russians and supplied by the German Army,

- 75mm Schneider field guns, Bulgarian or captured from the Serbians,

- 75mm Krupp field guns, captured from the Turks.

To these guns, we can add 80mm De Bange slow firing field guns captured from the Serbians, used briefly in the 2nd a/a battery, and the 88mm Krupp anti-aircraft guns used by the German Army to protect the sea-shore of Black Sea.

75mm Schneider gun mounted on the special Rakovski platform	75mm Krupp gun mounted on an improvised a/a platform	75mm mountain guns firing in a/a role