Bulgarian Artillery in WW1

[MCP]

In my inquiry about Bulgarian Artillery I have often found a reference to this article (I hope I typed correctly):
Яко Молхов, “Българската артнлерна през Балканската война (1912 г.)",
Военнои рически сборник, 57/1 (1988)
It seems very interesting, but - of course - I could not find it in Italy. If somebody has the chance to meet with it somewhere I greatly appreciate if he can make a copy for me.
Thanks.

[MCP]

The Russo-Japanese War and the development of Bulgarian Artillery

The Russo-Japanese War (1904-05) had a significant impact on the Balkan States Armies. The Bulgarian General Staff had sent a special military mission to Manchuria in order to become acquainted with special features of the conduct of military operations. Moreover a number of Bulgarian officers accompanied the Russian forces as volunteers. May be interesting to remember that Lt. Dimitar Dobrev, who in 1912 commanded four Bulgarian torpedo boats in the attack that damaged the Ottoman cruiser Hamidie in Black Sea, was present at the naval battle at Tsushima in May 1905.

The Russian defeat caused great concerns among the Balkan states because of concerns about their and national security. They realized that Russian help might not be available to reach their national aspirations against Ottoman Empire. But the Russo-Japanese War had not only a political and diplomatic influence. The military repercussions of the war were based upon Japanese success. This placed Bulgarian Army in a bad situation. The Bulgarian Army owed its formation and much of its doctrine and character to the Russian. Many senior Bulgarian officers had received their military education in Russia. In front of the defeat of its military model, Bulgarian Army began to deviate from Russian military systems and to adopt some ideas from the winner Japanese Army.
The most important acquisition for Bulgarian Army was the cult of bayonet attack, that would make famous Bulgarian infantry during Balkan Wars, but cause so many victims. But the experiences of the Russo-Japanese War were also very instructive in tactical use of artillery. The Bulgarian General Staff issued new instructions in 1906 for field and fortress artillery that incorporated some lessons taken from the the Russo-Japanese War.
First, instead of taking open positions and shooting directly towards the targed, field artillery now has to take deep masked positions. This was of great importance because of the irregular topography of much of the Balkan Peninsula, and expecially of the Bulgarian borders with Serbia and Turkey.

Another important lesson was the demonstration that siege artillery could be used not only against fortress and fortified positions, but also against field positions. For this purpose Bulgarian Army began to buy heavy artillery. Before the Russo-Japanese War, the Bulgarian Army had acquired only thirty 120mm Krupp howitzers old pattern, received about 1903. They are mobile and were distributed for war in five batteries assigned to first line troops. However initially they were attache to the Fortress Artillery and not to Field Artillery. Another twenty-four 150mm Schneider howitzers were received in 1904. But in order to increase their rate of fire, in 1907 some accessories were orderd. They were too attached to fortress artillery. In order to provide Field Army with a modern mobile heavy howitzer, Bulgarian General Staff in 1907 orderd thirty-six 120mm Schneider quick firing howitzers. They were formed into 9 batteries of 4 guns and 12 ammunitions wagons and were attached to Field Artillery. Every Army Inspectorate received a battalion composed by three batteries. In wartime they would have to support Field Army, expecially in order to destroy enemy batteries with indirect fire.
After 1905 the Bulgarian Artillery also began to buy quick firing guns. Taking into account the broken terrain of great part of its future theater of war, Bulgarian General Staff paied great attention to mountain artillery. After having obtained fifty-six 75mm Krupp quick firing guns, it ordered another thirty-six more modern Schneider quick-firing guns of the same calibre. At the beginning of the Balkan War, Bulgarian Army had 23 batteries of modern pack artillery, more that twice the number of the batteries owned by Serbian (9) or Greek (8) Army. Balkan Wars, fought mainly in the hills and mountains of Thrace and Macedonia proved the usefulness and the power of the fire of pack artillery.

One idea stemming from the Russo-Japanese War ignored by Bulgarian army was the efficient use of cavalry. In fact during the war the Japaneses failed to use their cavalry to harass the disorganized retreat of their enemy. They expecially failed to utilize the cavalry as a source of firepower. The admiration for the Japanese Army and the progressive adoption of its tatics may explain why Bulgarian Army did not provide its cavalry with artillery. This was a great weakness for it during the war against Turkey.
The need to utilize the new weapons effectively and to take advantage of the lesson of the Russo-Japanese War lead to the issue of new instruction for quick fire field artillery and for combat regulations for fortress artillery. They were published in 1908.

[MCP]

Rumenian captured guns

Gun model : Gruson 53mm
Calibre : 53mm
Weight: 564 kg
Tube Lenght :
Shell Weight : 1.66 kg
Muzzle Velocity :
Max. Range : 2740 m
Elevation :
Ammunition :
Remarks : Quick firing gun. Rumenians removed many of them and used them as light trench guns. Bulgarian Army used some of the 53mm guns captured in Tutrakan.

Gun model : Krupp 75mm QF M. 1903
Calibre : 75mm L/30
Weight in action: 1070 kg
Tube Lenght : 2.250 m
Shell Weight : 6.5 kg
Muzzle Velocity : 500 m/s
Max. Range : 8000m
Elevation : + 16° / - 8°
Traversing angle : 4°
Thickness of shield : 4 mm
Remarks : Quick firing field gun, very similar to the Krupp field gun adopted by Turkish Army.

Gun model : Krupp 105mm QF M. 1912/16
Calibre : 105mm L/14
Weight in action : 1155 kg
Tube Lenght : 1.470 m
Shell Weight : 15.7 kg
Shrapnel Weight : 14 kg
Muzzle Velocity : 300 m/s
Max. Range : 6500 m
Elevation : + 43° / - 5°
Traversing angle : 6°
Remarks : Quick firing light field howitzer. Bulgarian Army used some of these howitzers.

Gun model : Krupp 105mm
Calibre : 105mm L/35
Weight: 1497 kg
Tube Lenght : 3,58 m
Shell Weight : 18.7 kg
Muzzle Velocity : 512 m/s
Max. Range : 10.120 m
Elevation :
Ammunition :
Remarks : Slow firing gun. It was also removed from the fortresses and placed in batteries. Bulgarian Army used some of these guns captured in Tutrakan.

[MCP]

British guns in Rumanian service

In 1916-17 British Army sent to Rumania these artillery weapons:
Ordnance 4.5-inch quick-firing field howitzers (114mm)
Ordnance 5-inch slow-firing field howitzers (127mm)
Ordnance 6-inch quick-firing field howitzers (152mm)
Ordnance 60-pdr. heavy guns (152mm)
I don’t know wether Bulgarian Army captured any of them.

[MCP]

French guns in Rumanian service

In 1916-17 French Army sent to Rumanian these artillery weapons:
Puteaux 75mm Mle. 1897 quick-firing field guns
Schneider-Ducrest 65mm Mle. 1906 quick-firing mountain guns
Rimailho 155mm Mle. 1904 quick-firing howitzers
De Bange 120mm Mle. 1878 L heavy guns
Schneider 155mm Mle. 1877/1914 L heavy guns
Schneider 155mm Mle. 1877/1916 L heavy guns
Duchene-Dumezil 58mm mortars
I don’t know wether Bulgarian Army captured any of them.

[MCP]

ex Rumenian fortress guns

Rumenian fortresses were armed with a of old pattern heavy and field guns.
There were:
Russian 152.4mm M 1877 Krupp and Obuchov guns
French 120mm Mle 1865 La Hitte heavy guns
French field artillery Mle 1870 La Hitte and 1875 Lahitolle
German 210mm Krupp mortars
German 150mm Krupp heavy howitzers and guns of various patterns
German 120mm Krupp heavy howitzers and guns of various patterns
German 120mm Gruson QF howitzers mounted in armoured cupolas
German 105mm Krupp heavy guns
German 87mm Krupp field guns
German 53mm Gruson QF guns in movable cupolas
French 37mm Hotchkiss light QF guns
British 37mm Vickers-Maxim QF guns
I consider only the guns that, according with the sources I have, Bulgarian Army used during the war.

[MCP]

ex Rumenian field and mountain guns

The guns and howitzers used by Rumenian Army at the beginning of World War I were generally very similar to those adopted by Bulgarian Army.
Field artillery used the same 75mm quick firing and 87mm slow firing Krupp guns. There were only some little improvements in the more recent M 1907/12 field gun.
It used also the same 105mm quick firing Krupp howitzers and 150mm Schneider-Creusot howitzers.
Mountain artillery used the same 75mm quick firing Krupp guns, and a little number of old (63.5mm Armstrong) or little (57mm Krupp) guns.
The old 120mm De Bange M. 1878 field howitzers were the same howitzers used by Serbian Army and captured and used by Bulgarian Army.
AFIK Bulgaria Army did not captured any Rumanian 240mm heavy gun or 210mm mortar.

[MCP]

Strenght of Rumanian Artillery in 1917

In winter 1916-17 Rumanian Army was reorganized by a french Military Mission It was composed by 1150 French officiers commanded by gen. Henri Berthelot. His chief of Staff was colonel Petin. Gen. Berthelot was integrated into the Rumanian Army general inspector’s staff. He had the title of "Adiviser attached to Rumanian High Command for the direction and the development of military operations". His mission begun at the beginning of December 1916, when he was was integrated into the Rumanian Army general inspector’s staff.
On 12 March 1918 the French Military Mission was expelled from Rumania by Germans. The number of the infantry divisions was reduced from 23 to 15. The artillery was provided by modern French quick firing guns and heavy guns and howitzers arrived from France and Great Britain. Also a little number of Russian guns was utilised. Everything had to come or via Murmansnk or Arkhangelsk, through the White Sea, a way that was useless in winther because of the ice, or via Vladivostok, in Siberia. But the major problem was the little cooperation of Russian authorities, that greatly delayed the arrive of weapons and equipments.
Col. Charles-Ernest Vouillemin was charged to the mission of reorganizing Rumanian Field Artillery, while Leit-col. Leon Steghens was assigned to heavy artillery. Col. Augustin Ungerer (Engineer Corps) had to train Rumanians in trench warfare. French artillery officiers were attached to Rumanian Armies :
1st Army : col. Pierre Henri Lafont
2nd Army : col. Paul-Joseph Marie

As for artillery the first aim of French Military Mission was the standarization of guns. The calibres adopted were:
field artillery : 75mm
mountain artillery : 75mm
light field howitzers : 105mm, 114mm
heavy field howitzers : 155mm and 152mm
heavy guns : 120mm and 155mm
trench artillery : 58mm mortars
There was a great need of heavy artillery. British Loyd George proposed to send in Rumania twenty-five 152mm howitzers, but only some of them arrived in Moldavia in September 1917 and most of them had been sabotaged by Bolsheviks. Waiting for them, Great Britain offered thirty-two 127mm old howitzers.

In mid June 1917 the four Infantry Divisions of 1st Rumenian Army had :
- 9 Field batteries with 75mm Krupp guns
- 2 batteries with 105mm howitzers
- 1 battery with 53mm light guns
- 1 battery with 58mm French mortars;
while the six Infantry Divisions of 2nd Army had :
- 9 Field batteries with 75mm Krupp guns
- 1 battery with 105mm howitzers
- 1 battery with 120mm howitzers
- 1 battery with 53mm light guns
- 1 battery with 58mm French mortars.
The remaining five Infantry Division had to be equipped with French Field guns (75mm Puteax), but only 63 guns had left France and had reached Rumania (some of them without their ammunition wagoons), while another 35 guns were still in Russia. The remaing guns were still in France.

In 1917 Rumanian Army had:
114 field artillery batteries
14 mountain artillery batteries
80 field howitzers batteries
2 heavy howitzers batteries
47 heavy guns batteries
15 trench mortars batteries.

[MCP]

Corrections and updates

Having found some new informations that I was waiting for, I added some datas and made some little corrections in posts 8, 11, 39.

[MCP]

Rumanian fortress in Dobrudja

Tutrakan (Turtucaia in Rumanian) was intensively fortified in 1913-1916 with the aid of Belgian military engineers. Although linked to Oltenita, directly across the Danube, by a submerged telephone cable and an array of small boats, this "bridgehead" had no bridge. These defenses, as yet unfinished in 1916, consisted of three concentric lines of defense, anchored on the Danube, with a radius of 8 km and a circumference of 35. The most advanced position, some 1000 meters deep, consisted primarily of small outposts of pickets designed for surveillance and to force an enemy to reveal his intentions. About four kilometers back, on the heights overlooking the city, was the primary line of defense. It incorporated 15 forts about two kilometers apart. These were mostly of earthen construction with only limited concrete. These forts were linked by a system of shallow trenches and protected by barbed wire obstacles. Four kilometers behind the primary line of resistance stood a primitive secondary line. It consisted of a single row of neglected trenches, partly collapsed, with some barbed wire but without artillery or machine guns. Its value was extremely limited.
For command purposes, the entire defensive system was divided into three sectors: I (west), II (south), and III (east), each with its own local commander. Most of the artillery the garrison possessed was in the primary line. Guns of light caliber predominated. Many of those of heavier caliber were not mobile and incapable of firing toward the flank or rear. Some were not yet operational and/or lacked shells of the correct caliber. Prominently represented at Tutrakan were ancient cannon salvaged from dismantled forts around Bukarest and the abandoned Focsani line on the ramparts of Moldavia.
The Danube was mined within a 7 km radius from the town. On the islands of Karnetschin, Tsokludsha and Kalimok tere were heavy machine guns and light QF guns in armoured cupolas.

On august 1916 Tutrakan fortified position was manned by the 17th Infantry Division, with 19 battalions, 66 machine guns, 29 batteries:
6 field artillery batteris with 23 - 75mm guns and 120mm howitzers with 17,088 shells;
23 fortress artillery batteris with 82 guns, howitzers and mortars (caliber from 75mm to 210mm) with 38,084 shells;
28 armoured turrets (some in a mobile armour carriages) armed with 53mm QF guns;
14 armoured turrets (some in a mobile armour carriages) armed with 37mm QF guns;
giving 55 - 53mm and 37mm light guns with 110,000 shell.
During the siege, on 4 and 5 September, the fortress received 4 batteries with 28 - 75mm and 105mm guns.

In order to defend the fortress from the attack of Austro-Hungarian Danube flottilla, along the Danube shore it was built the "Turtucaia Position", utilising naval guns from the decommissioned cruiser Elisabeth as well as her torpedo tubes. This strongpoint was armed with:
4 -150mm L/35 Krupp guns old pattern;
4 - 120mm Schneider-Creusot L/45 guns;
4 - 75mm Schneider-Creusot L/50 guns;
4 - 356mm torpedo tubes.
After the fall of Tutrakan, the Romanians were forced to abandon the "Turtucaia Position" under pressure from advancing and encircling forces of the Central Powers. The main guns were removed to Galatz, where they briefly shelled German batteries before being lost during the retreat on December 1916.

Silistria, like the other Bulgarion fortress along the Danube - Vidin, Ruse, Shumen - was surrounded by a bastioned line with an old citadel and small forts at the point where these lines abut on the Danube. it had little military value. In 1913 Rumanians begun to reinforce and modernize it, but in august 1916 the defeces are not completed.
On august 1916 Silistria fortified position was manned by the 9th Infantry Division, with 16 battalions, 66 machine guns, 17 batteries:
12 field artillery batteris;
3 fortress artillery batteris;
17 armoured turrets (some in a mobile armour carriages) armed with 53mm QF guns.
Excepting the field artillery, there were 76 light and heavy guns in Silistria fortress.

The Cernavoda bridge-head in august 1914 had a garnison of two Infantry battalions with 27 machine guns and 11 fortress batteries and a dozen of armoured turrets.

[MCP]

Rumanian fortifications

In 1913, at the end of Interallied War, in Rumania there were two great systems of fortifications :
1. the forts around Bukarest which convert the capital to a great entrenched camp.
2. the works constructed on the line of the River Sereth, directed against an advance from the east and northeast.
In addition, in Dobrudja there was a bridge-head at Cernavoda guarding the railway bridge over the Danube.
In 1914-16 some guns and howitzers were used to arm the newly aquired fortress of Silistria and the so-called Tutrakan bridge-head, to build the siege artillery batteries and to reinforce divisional artillery with 53mm QF guns.

The fortifications of Bukarest consisted of 18 detached forts with 18 intermediate batteries, situated at an average distance of 9.5 km from the centre of the town. The total perimeter was around 72 km. The forts were commenced in the year 1885, and completed and fully armed in 1896. The original scheme was prepared by General Brialmont, but it was considerably modified in order to reduce the cost. A circular railway, with a military road and a telegraph or telephone line alongside, conneced all the forts.
The forte are situated as follows :
- on the left bank of the Dambovita river: Chitila, Mogosoia, Otopeni, Tunari, Stefanesti, Afumazi, Pantelimon, Cernita and Cotzelu.
- on the right bank of the Dambovita river: Leordeni, Popesti, Berceni, Jilava, Broscariu, Magurele, Bragadir, Domnesti and Kiaina.
The works were of six different types, and their armament varies accordingly. They were constructed to resist high explosives, and armour has been largely used. The majority bave dry ditches. The intermediate batteries were armed with 120mm guns and howitzers. The armament of the forte consisted of 150mm guns, 210mm howitzers and 53mm quickfiring guns. All were mounted in turrets or cupolas, the 150mm guns in pairs, the remainder singly. As a rule, the forts had 3 - 150mm guns, 3 / 4 howitzers, and 4 / 6 quick-firing guns.
The works was manned by Fortress Artillery Regiment with headquarters at fort Chitila. The fortifications were commanded by the Governor of Fortress of Bukarest, in august 1916 Div.Gen. Mihail Boteanu.

The fortified line of the Sereth, covering a front of about 72 km, consisted of the entrenched camps of Galatz in the southeast and Focsani in the north-west respectively, and of the bridge-head of Nomoloasa at the centre.
The fortifications were commenced in the year 1889 on a plan prepared by Major Schumann of the Gruson Works, and were completed in 1893.
The fortified region was commanded by of a general of division, in august 1916 Div.Gen. Petre Nasturel with headquarters at Galatz. Many of the guns in 1914 were moved from the forts in order to arm the Siege artillery Regiment.

The fortifications of Galatz are on the left bank of the Danube, at some distance from the river. There were 10 groups of works arranged in 3 lines with frontal and flank defence. The total extent of front was 14.5 km.
The names of the groups are Sereth, Sendreni Malina, Barbosi, Smardan, Covureni, Filesci, Trajan, Raves and Brates.
There were a total of 51 batteries. The armament of the first and second lines was composed of 53mm. QF guns, the guns of the first line were on travelling carriages mounted in concrete emplacements in groups of three, those of the second line were mounted in small disappearing turrets, six being grouped together to form a battery. The third line had armoured batteries of 120mm Gruson howitzers mounted in pairs, but three batteries had three howitzers, and one battery four. The works were manned by 1st Fortress Artillery Battalion.

The Nomoloasa works were upon the left bank of the Sereth. The bridge-head covered several bridges, and barrred the Jassy-Galatz road and railway.
The works, arranged in two lines, consist of 8 groups situated about 9.5 km from the town of Nomoloasa with a total extent of front of 11 km. There was an interval of about 1,000 to 1,400 yards between the groups, each of which had 2 / 3 batteries in the first line and 2 in the second line. There were a total of 30 batteries.
The names of the groups were: Calieni, Serbanesti, Tecusi, Calmatnin, Mikai-Braoul, Tudor Vladimerescu, Galati and Conachi. The armament was 53mm QF guns on travelling carriages, in the first line, 3 for each group, and 120mm howitzers in pairs in armoured turrets for the second line. The total armament was 72 - 53mm guns and 16 - 120mm howitzers. The works were manned by 2nd Fortress Artillery Battalion.

The entrenched camp of Focsani was on the right bank of the River Putna, a tributary of the Sereth, and barrred the
road and railway Roman-Buzeu-Bucharest. The general trace of the works is a semi-circle, with a total extent of about 21 km, and distant about 6.5 to 9.5 km from Focshani.
The works are arranged in 3 separate lines giving frontal and flank defence, and numbered 71 batteries, distributed in 15 groups and 1 independent group (first line - 41 batteries, second and third line 15 batteries each).
The names of the groups were Odobeshti, Vrancea, Pancia, Baia, Marasesci, Resbviene, Furceni, Petresce, Venatori,
Putna, Jorasti, Siefan Cel Mare, Mandresti, Braila, and Milcov. The works of the first line were converted emplacement armed with 37mm QF guns on travelling carriages, each battery having five guns. The second line was armed with 53mm QF guns in disappearing turrets arranged 6 to a battery. The batteries of the third line contained one 120mm Krupp gun and two 120mm howitzers. The independent group to the north-west of Focshani, covering a crossing over the River Putna, contained 4 Gruson 120mm howitzers.
The total armament was 214 - 37mm guns, 90 - 53mm guns, 15 - 120mm Krupp guns and 34 -120mm Gruson howitzers. The entrenched camp was manned by 3rd Fortress Artillery Battalion.

The Cernavoda bridge-head was constructed on the right bank of the Danube to the south and east of Ceruavoda. It was built in the year 1900, and contained an armament of 53mm QF guns, 105mm Krupp guns and 87mm Krupp field guns.
The works were arranged in three lines, and were divided into two groups by the railway line. The first line was 9 miles in extent and distant 35 miles from the railway bridge, and consisted of a line of infantry entrenched positions and redoubts. The second line had 6 batteries, 3 to each group, while the third line consisted of field artillery redoubts constructed to take 18 guns. The bridge-head was manned by a detachment of Fortress Artillery.


From GENERAL STAFF, WAR OFFICE, Military Notes on the Balkan States, 1915, pages 20-24

[MCP]

Rumanian captured guns

In 1914 at the outbreak of world War I Rumanian Army had:
1 horse artillery regiments with 24 - 75mm Krupp M. 1904 and M 1907/12 QF guns
25 field artillery regiments with 600 - 75mm Krupp M. 1904 and M 1907/12 QF guns
(ASIK there were 396 - 75mm Krupp M. 1904 and 228 75mm Krupp M. 1907/12 QF guns)
426 - 87mm Krupp M. 1886/97 slow firing field guns
6 mountain artillery batteries with 16 - Krupp 75mm M. 1904 QF guns
6 mountain artillery batteries with 24 - 63.5mm Armstrong slow firing guns
3 mountain artillery batteries with 12 - 57mm Krupp QF guns
5 field howitzers regiments with 120 - 105mm Krupp M. 1898/09 and M 1912 QF howitzers
4 field howitzers division with 32 - 120mm De Bange M. 1878 field howitzers
1 field howitzers division with 8 - 150mm Schneider-Creusot howitzers
1 Siege Artillery Brigade with three regiment armed with:
60 - 105mm Krupp, 150mm Krupp and 155mm De Bange heavy guns
15 - 240mm Armstrong heavy guns and 210mm Krupp mortars
1 fortress artillery regiments with 2 battalions (11 fortress and 2 depot companies)
3 indipendent fortress artillery battalions (12 fortress and 3 depot companies)
There were also 26 field artillery depot batteries, 1 mountain artillery depot battery, 105mm howitzers depot sections and a 150mm howitzers depot section.

In august 1916 Rumanian Army could field 374 batteries, of whom 233 were armed with quick firing guns. In order to the strenght of quick firing field artillery most of the 53mm and 57mm fortification guns were removed from their positions, fitted with improvised carriages and issued to newly-raised batteries (6 armed with 57mm and 50 with 53mm Gruson QF guns). There were also 113 antiaircraft guns converted from field guns of various calibers (53mm, 57mm, 75mm).

During the 1916 campaign Rumenian Army lost at least 450 guns and howitzers, of them almost 150 were captured by Bulgarian Army in Tutrakan (for Rumanian fortress see next post). Some other guns were captured in Silistria and during the pursuit to Bukarest. Since artillery materiel used by Rumanians was generally the same used by Bulgarian army, it is very likely that some of the guns captured were used by Bulgarians. I have at least one evidence of this, since Nikola Nedev in his book about Doiran adfirms that in 1918 1st Makedonska Brigade used two 105mm heavy guns captured in Tutrakan (page 243 of the french edition).

[MCP]

Strenght of Serbian Artillery in Macedonia during the war

Today I have noticed that I had forgot to send the message about the strenght of Serbian artillery after its defeat in 1915. I add it now, even if it not in the correct place. Sorry. :shrug:


Serbian troops evacuted to Corfu between 18 January and 23 February 1916 were organized by a French Military Mission commanded by gen. de Mondesir. Serbian Army was organized into six infantry divisions and one cavalry division based on the French model. France had to provide armament, artillery, equipments and animals. Great Britain gave clothings and transport animal and lorries. When Serbian reached Solun gen. de Mondesir went back to France, but french and British officers remained with them.

Each Infantry Division would have :
one artillery group with three Field Artillery batteries (four 75mm QF guns each);
one artillery group with three Mountain Artillery batteries (four 70mm or 65mm QF guns each);
one artillery group with three Mountain Artillery batteries (four 80mm not QF guns each);
one artillery group with three Field Howitzer batteries (four 120mm QF howitzers each);
one battery with six 58mm light Mine launchers.

On April-May 1916, when the Serbian Army was assembled in Solun area, it was complete in transport and artillery:
9 field artillery groups;
8 mountain artillery groups;
6 field howitzers batteries;
some light Mine launchers.

On September 1918 the Serbian Army had:
113 70mm and 65mm QF mountain guns;
116 75mm QF field guns;
2 105mm QF heavy howitzers (captured);
54 120mm QF 120mm howitzers;
1 150mm QF howitzer (captured);
3 captured guns (caliber not known).

During the offensive in 1916 and 1917 Serbian Army was supported by French heavy guns.

[MCP]

The occupation of Eastern Macedonia

At the beginning of August 1916, when Bulgarian Army became its advance, the Fortress of Kavala was not in good condition. The fortification works had not been finished. Of the five forts covering Kavala, only three were completed, of the ninety guns that had been planned for the fortified positions, there were only two obsolete naval guns, and of the 2,000 gunners foreseen there were only 140. The infantry for the defense of the forts, which should have been five regiments, was entirely missing. The machine guns only then had begun to be placed in their positions. The Fortress Command was tasked largely with the supervision of works under construction rather than the conduct of war. Its force numbered thirty-five officers and 250 enlisted men.

Since the negotiations with the Allies were inconclusive, Greek government decided not to resist the German-Bulgarian invasion and on 15 August ordered Kavala Fortress to withdraw the guns and machine guns from the fortified positions. The 7th Artillery Regiment transported the armaments of the forts of Lisse, Perithori and Tulunbar to Drama.
On 18 August the screening companies of 5th Division in the area of Drama were withdrawn. A few outposts that remained were captured by the Bulgarians. 5th Division assumed a defensive deployment, but on the evening of the same day, Army Corps D received from the Minister of the Army General Konstantinos Kallares the order to avoid any kind of friction with Bulgarian army: if 5th Division was unable to remain in Drama, it had to withdraw to Kavala.
On 19 August in the zone of responsibility of 6th Division, the Bulgarians attacked Greek troops and after a brief negotiation two companies based in Achladochori and Phaia Petra were disarmed by the Bulgarians. However the mobilization equipment and armament of 6th Division was not captured because it had been sent to Old Greece.
On 20 August 2nd Trakiska Infantry Division captured the forts of Lisse and Perithori. The materiel of the forts was scattered by the Bulgarian cavalry while being transported to Drama. Since one Bulgarian column was approaching the forts round Kavala, 7th Division was ordered to defend them. The following day the commander of Army Corps D, Colonel Ioannes Chatzopoulos, received the order to avoid the use of force. In meantine, between 19 and 22 August the advancing Bulgarian troops drove back the Greek forces inside Eleutheroupolis, Siderokastro, Serres, Drama, and Kavala, cutting off all the communications and capturing the whole of eastern Macedonia.
On 23 August Army Corps D ordered 5th Division to leave Drama and to relocate to Kavala, but this movement was postponed since the provisioning of the Division would be easier in Drama. The same day the Bulgarians demanded the to capture "D" (= Delta). While the commander of Army Corps D was waiting for istructions from its government, the Bulgarian captured both forts "D" and "E" (= Epsilon).
On 24 August 10th Belomorska Infantry Division captured the heights around Eleutheroupolis and tightened the encirclement of Kavala with the capture of saddle of Stauroupolis and forts "I" (= Iota), "Z" (= Zeta), and "H" (= Heta). The following day they captured the remaining forts.
On 1 September, being not able to restore contact with Army Corps D and the government, 6th Division, which was encamped in Nea Zichne, minus the 16th Infantry Regiment, departed for Kavala, arriving there on 4 September after passing through Eleutheroupolis and the forts captured by the Bulgarians.

On 3 September 1916 the general situation in eastern Macedonia was as follows:
-- 5th Division in Drama, the 16th Infantry Regiment of 6th Division in Serres and the 20th Infantry Regiment of 7th Division in Eleutheroupolis were encircled by the Bulgarians;
-- 6th Division VI, minus the 16th Regiment, was moving towards Kavala;
-- the forts of Kavala had been captured by 10th Belomorska Infantry Division;
-- the commander of Army Corps D sent repeated telegrams requesting that the equipment be transported to Old Greece;
-- fifteen rebel officers of the Kavala garrison, following an order issued by the Committee of National Defense, went from Thessalonica to Thasos in order to spread the revolt to 6th Division.
Faced with this situation the Ministry of the Army ordered that 5th and 6th Division, along with the non-divisional units of Army Corps D, assemble in Kavala, but this was impossible for those units that continued to be encircled by the Bulgarians.
On 6 September Colonel Hristo Burmov, the commander of 10th Belomorska Infantry Division, and the German lieutenant Schmidt requested of the commander of Army Corps D to be allowed to occupy the heights north of Kavala, in order to defend against a possible landing by the Allies. The Corps commander, having no other choice since the orders of the government called for the avoidance of any kind of friction, was forced to succumb and to evacuate those heights. Thus, the garrison of Kavala was confined to the city, with no possibility of defense. In the meantime the commander of 6th Division was persuaded to move his troops to Solun on Allied ships and to accede to the National Defense movement, in order to avoid their capture by the Bulgarians.
On 9 September, the British landed a Marine detachment in Kavala which destroyed the wireless of the city. Army Corps D was now cut off from the government and Kavala was blockaded by land and by sea. That night Allied transport vessels sailed into the harbor secretly to transport the men of Division VI to Thessalonica, but the commander of the Corps blocked the departure. Only fifteen officers and fifty enlisted men managed to leave by boat to Thasos.
On 10 September 1916 in a meeting with German major von Schweinitz, the commander of the Corps in order to avoid the capture of its troops by Bulgarian forces, asked wether German High Command could guarantee the transportation of the Army Corps, along with its armament, to Germany and its stay there. Major von Schweinitz promised to submit the proposal. An attempt to escape during the night of 9-10 September throught British ships failed because the commander of Army Corps D refused to join the National Defence moviment.
On 11 September the corps commander met again Major von Schweinitz, who delivered to him the reply of Field Marshal von Hindenburg: he accepted the transfer of the Army Corps D to Germany with its armanents. The men of the Greek forces would not be considered prisoners but rather guests of the Germans. During the night of 11-12 September the garrison of Kavala - 400 officers and 6000 enlisted men - moved towards north. All materiel - except 7th Artillery Regiment - was abandoned in Kavala and fell into the hands of Bulgarian Army. Part of the Greek fortress artillery was used by 10th Infantry Division for coast defence.

Remarks:
a good map of Bulgarian advance in Struma valley is attached by Parabellum at http://forum.boinaslava.net/showthread.php?t=5528
However I add a Greek map since it show with more detail the position of Greek and Allied Forces.

[MCP]

The Capture of Rupel fort

On 10 May 1916, the German Militar attache in Athens announced to the Greek government that the German Staff deemed necessary the occupation of the Rupel pass because the Etente forces had crossed the Struma river. The Greek government protested to Berlin immediately but on 22 May the German and the Bulgarian ambassadors in Athens notified that their forces were going to occupy the Rupel pass. They stated that they would respect the integrity of the country, but the continuing offensives of the Entente forces compelled to a quick reaction.
The threatened area was occupied by Army Corps D with 7th Infantry Division in Kavala, 6th Infantry Division in Serres and 5th Infantry Division in Drama. The forts of Rupel, Phaia, Petra, Perithori had been attached to 6th Infantry Division, that was at full-strength. On 24 May the French captured the fort of Kastanousa, north of Kilkis, and two days later the Germano-Bulgarian became their advance towards Rupel.
Solun Fortress Command, quickly informed by Major Ioannes Maouroudes, the commander of the fort, ordered to present a vigorous defence. Therefore the commander of the 6th Infantry Division deployed his troops in order to obstruct the passage to the Bulgarian Army and notified the Entente forces if they wished to intervene. At the same time the Germano-Bulgarian went on advancing and notified to Greek screening troops that they had the order to capture fort Rupel. But when Major Maouroudes gave the gun on order to fireat the head of the ennemy’s column, the Germano-Bulgarian forces halted their movements and withdrew beyond the frontier.
Only tventy-five minutes later, at 15.05, the commander of 6th Infantry Division, Major General Andreas Bairas, received from Athens the order that resistence should not be offered and the screening troops were obliged to withdraw without engaging in battle. He immediately gave the order to cease all resistence and at 19.00 two Bulgarian battalions encircled fort Rupel and demanded its immediate surrender. Major Maouroudes refused, but the commander of the Bulgarian detachment answered that the garrison was obliged to evacuate the fort during the night, otherwise it would be isolated.
At 05.00 on 27 May Major Maouroudes met German Cavalry Captain Thiel, who accepted the surrender of the fort and all the equipment that would remain in it. At the same time the ordnance of the fort was quickly loaded on the vehicles sent by the Command of the 6th Infantry Division and it and the garrison departed for Siderokastro. The materiel that remained in the fort was captured by Bulgarians.