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Description
EDIT, 17.04.15: added layer texture to the concrete.

This is the second of nine drawings made for the book "The Fortified Region Focsani-Namoloasa-Galati" about the eponymous Fortified Line (also known in English as the "Sereth Line" and by it's abbreviation "FNG") built by Romania for defence against a presumptive Russian invasion during 1888-90.

Making full use of the natural barriers of the Carpathian Mountains to the west and the River Danube to the east in order to protect its flanks, the line was constructed along the bank of the Siret (Sereth) River in southern Moldova and consisted of three distinct fortified areas, each protecting the main river crossings. Around the town of Focsani in the west, in the foothills of the Carpathian Mountains; in the middle around the village of Namoloasa and finally around the port town of Galati, on the bank of the Danube.

The drawing shows the 3.7cm Schumann-Gruson Fahrpanzer (a shortening of "fahrbaren Panzerlafette", "mobile armour"), a type of late 19th century mobile gun turret whose role was to combat enemy infantry attacks.

They were the brainchild of Prussian tactician and fortification engineer Maximilian Schumann who, critical of the "mainstream" school of fortification of the time which favoured large, heavily armed forts set far apart, instead envisaged a style of fortification made out of small forts set close together in successive lines to give a fortified position "defence in depth" and better control the intervals.
Since this was before the advent of the machine gun, he decided small calibre quick firing guns were the the best way to combat infantry, and he designed a system of small turrets who could be deployed quickly to the needed position either by narrow gauge railway or horse drawn cart and installed into prepared concrete positions or hastily dug pits according to what the tactical situation requires.

The turrets themselves were manufactured by the weapons factory belonging to German industrialist Hermann August Jacques Gruson and exist in three successive types, all of which were used on the Focsani-Namoloasa-Galati line.

This is the smallest, the 3.7cm Md.1887 turret which was the first to be manufactured and was only used in the forts of the Focsani. 225 of them were imported and were deployed to the first line batteries in batches of five as well as to guard the flanks of the second line batteries in batches of fourteen.

The whole turret is 1.42 meters tall, 1.21m in diameter and weighed just over a metric ton - 1,022kg.
Out of these, 344kg are in the cupola itself, which is hemispherical and made out of 25mm thick steel.
The turret body is made out of 3mm thick wrought iron strengthened around the upper part with a 25mm ring also of wrought iron.

The cupola could be manually traversed 360° and the gun had an elevation of -5° and +10°. Ammunition provision was five ammo lockers with 20 rounds each (completely insufficient for any sort of prolonged action), while the gun crew consisted of two - one captain/gunner and an assistant, who's duty was to keep the turret supplied with ammunition by going outside to the masonry ammunition stores set between the cupola emplacements. Needless to say, that would have been a most likely suicidal proposition during actual combat.

For transport, the fort used the pictured horse drawn carriage, one for each three turrets and with a crew of four to manhandle the turret into it's waiting emplacement (note that visible in the background on the left is the 5.3cm disappearing cupola position ).

Said emplacement consisted of a horseshoe shaped casemate made out of unreinforced concrete and further protected by a glacis of packed earth in the direction of the enemy.
Unfortunately, since in the 19th century the use of concrete was still pretty much hit and miss, the concrete (with the mix ratio of 1:2:4 per volume, or 1 mark of cement, 2 of sand and 4 of aggregate) used during the construction of the FNG fortifications proved to be of very poor quality and would probably have fared badly in combat, due partly to improper pouring techniques as well as an inconsistent mix ratio of aggregates between batches which created highly distinct layers into the concrete mass instead of a single monolithic block.

EDIT: the only known surviving example of a 3.7cm Fahrpanzer can be found at the military museum in Copenhagen.

The other drawing in this series can be found here:

Cover, showing cutaway through 5.3cm mobile gun turret
Plate I, the 3.7cm mobile gun turret and transport carriage.
Plate II, the 3.7cm gun and ammunition.

Plate III, the 5.3cm mobile gun turret in its concrete emplacement .
Plate IV, the 5.3cm mobile gun turret in transport configuration.

Plate V, the 5.3cm disappearing cupola.

Plate VI, the 5.3cm gun and ammunition.

Plate VII, the 12cm gun and mortar armoured battery.

Plate VIII, the 12cm gun and mortar and their ammunition.

Description
EDIT, 17.04.15: added layer texture to the concrete.

This is the second of nine drawings made for the book "The Fortified Region Focsani-Namoloasa-Galati" about the eponymous Fortified Line (also known in English as the "Sereth Line" and by it's abbreviation "FNG") built by Romania for defence against a presumptive Russian invasion during 1888-90.

Making full use of the natural barriers of the Carpathian Mountains to the west and the River Danube to the east in order to protect its flanks, the line was constructed along the bank of the Siret (Sereth) River in southern Moldova and consisted of three distinct fortified areas, each protecting the main river crossings. Around the town of Focsani in the west, in the foothills of the Carpathian Mountains; in the middle around the village of Namoloasa and finally around the port town of Galati, on the bank of the Danube.

The drawing shows the 3.7cm Schumann-Gruson Fahrpanzer (a shortening of "fahrbaren Panzerlafette", "mobile armour"), a type of late 19th century mobile gun turret whose role was to combat enemy infantry attacks.

They were the brainchild of Prussian tactician and fortification engineer Maximilian Schumann who, critical of the "mainstream" school of fortification of the time which favoured large, heavily armed forts set far apart, instead envisaged a style of fortification made out of small forts set close together in successive lines to give a fortified position "defence in depth" and better control the intervals.
Since this was before the advent of the machine gun, he decided small calibre quick firing guns were the the best way to combat infantry, and he designed a system of small turrets who could be deployed quickly to the needed position either by narrow gauge railway or horse drawn cart and installed into prepared concrete positions or hastily dug pits according to what the tactical situation requires.

The turrets themselves were manufactured by the weapons factory belonging to German industrialist Hermann August Jacques Gruson and exist in three successive types, all of which were used on the Focsani-Namoloasa-Galati line.

This is the smallest, the 3.7cm Md.1887 turret which was the first to be manufactured and was only used in the forts of the Focsani. 225 of them were imported and were deployed to the first line batteries in batches of five as well as to guard the flanks of the second line batteries in batches of fourteen.

The whole turret is 1.42 meters tall, 1.21m in diameter and weighed just over a metric ton - 1,022kg.
Out of these, 344kg are in the cupola itself, which is hemispherical and made out of 25mm thick steel.
The turret body is made out of 3mm thick wrought iron strengthened around the upper part with a 25mm ring also of wrought iron.

The cupola could be manually traversed 360° and the gun had an elevation of -5° and +10°. Ammunition provision was five ammo lockers with 20 rounds each (completely insufficient for any sort of prolonged action), while the gun crew consisted of two - one captain/gunner and an assistant, who's duty was to keep the turret supplied with ammunition by going outside to the masonry ammunition stores set between the cupola emplacements. Needless to say, that would have been a most likely suicidal proposition during actual combat.

For transport, the fort used the pictured horse drawn carriage, one for each three turrets and with a crew of four to manhandle the turret into it's waiting emplacement (note that visible in the background on the left is the 5.3cm disappearing cupola position ).

Said emplacement consisted of a horseshoe shaped casemate made out of unreinforced concrete and further protected by a glacis of packed earth in the direction of the enemy.
Unfortunately, since in the 19th century the use of concrete was still pretty much hit and miss, the concrete (with the mix ratio of 1:2:4 per volume, or 1 mark of cement, 2 of sand and 4 of aggregate) used during the construction of the FNG fortifications proved to be of very poor quality and would probably have fared badly in combat, due partly to improper pouring techniques as well as an inconsistent mix ratio of aggregates between batches which created highly distinct layers into the concrete mass instead of a single monolithic block.

EDIT: the only known surviving example of a 3.7cm Fahrpanzer can be found at the military museum in Copenhagen.

The other drawing in this series can be found here:

Cover, showing cutaway through 5.3cm mobile gun turret
Plate I, the 3.7cm mobile gun turret and transport carriage.
Plate II, the 3.7cm gun and ammunition.

Plate III, the 5.3cm mobile gun turret in its concrete emplacement .
Plate IV, the 5.3cm mobile gun turret in transport configuration.

Plate V, the 5.3cm disappearing cupola.

Plate VI, the 5.3cm gun and ammunition.

Plate VII, the 12cm gun and mortar armoured battery.

Plate VIII, the 12cm gun and mortar and their ammunition.