Russian antiaircraft guns

According История на зенитната артилерия… , p. 22 in 1917 the Bulgarian Air Defence received from Germany at least 12 “special Russian anti-aircraft gun” (специално 7,62-см руско противоаеропланно оръдие). They were 76.2mm Russian guns seized as trophies by German Army. These were the only real anti-aircraft guns used by Bulgarian Army during World War 1. All others guns were in fact modified field guns on improvised mounting. This sound very strange. According with Nicholas GOLOVINE, The Russian Army in the World War, “Economic and social history of the world war. Russian series”, New Haven, Yale Univerity Press, 1931, during the war Russian produced only 20 anti-aircraft guns (the so called “Lender’s guns”), and received another 36 anti-aircraft guns from its allies. But I think there is a convincing solution for this problem.

By spring 1915 German Army begun to use anti-aircraft artillery converted from captured guns.

The French 75mm M. 1897, the standard gun of French field artillery, had its barrels rebored by Krupp to 77mm in order to take German standard 77mm ammunition and became 7,7cm Bak L/35. Until the end of the war more than 400 of these guns served with German Army. BaK batteries using this gun were furnished with all captured French equipment, including limbers and caissons.  The system served in all theatres, and remained in use throughout the war.

The same happened with the 76.2mm Putilov M. 1900 and M. 1902 field guns. Russian guns could not be rebored due to the brittle barrels, so they kept their 76.2mm calibre, and when the captured ammunition had been used up, new replacements were manufactured in Germany. They were mounted on pedestals or on trucks of various patterns:

7,62cm Ortfeste Flak L/30 (russ 02) : 220 guns manufactured by Rheinmetall;

7,62cm Wagenflak L/30 (russ 02) : 28 guns manufactured by Rheinmetall;

7,62cm Eisenbahnflak L/30 (russ 02) : a few guns manufactured by Rheinmetall at the beginning of 1915;

7,62cm Räderflak L/30 (russ 00) : 60 guns manufactured by Krupp between December 1916 and March 1917;

7,62cm Räderflak L/30 (russ 02) : 120 guns manufactured by Krupp between March and June 1917;

7,62cm Sockelflak L/30 (russ 02) : 120 guns manufactured by Krupp between December 1917 and March 1918;

7,62cm Ortfeste Flak L/30 : 48 guns manufactured by Krupp in late 1918;

7,62cm Raupenflak (russ 02) : 4 trucks with two guns each manufactured by Krupp in 1918.

What kind of Russian Flak did Bulgaria receive during the war? The gun in the picture below is very similar to the Sockelflak. This is even more likely, since at least two 76.2mm QF Flak received by Bulgaria were designed “на цокъл”, that is exactly the translation of “auf Sockel”. But, since the production of this gun begun only in late 1917, the first group of Russian Flak, received in July 1917, were gun of older pattern, probably Rheinmetall Ortfeste Flak.

In order to learn the use of the 76.2mm anti-aircraft guns given by German Army, from 29 April to 25 May 1917, the commander of 2^nd and 3^rd a/a batteries - Lt. Stefan Oreshkov and Cpt. Bogdan Bonev - who spoke German and French, attended a course at Blankenberg (Germany). In the second half of 1917 a group of officers and NCOs attended a one month course at the school of Gent (Belgium). In the same period Col. Rakovski made a one month tour in Germany, in order to learn the organization of fire of German artillery.

The so called “special Russian anti-aircraft gun”