side,
Bucharest On the night of 27 August 1916, three Romanian armies (
First,
Second and ), deployed according to the Romanian campaign plan (
Hypothesis Z), launched the
Battle of Transylvania through the
Carpathians. On that same night, the torpedo boats ,
Bujorescu and
Catinca attacked the Austro-Hungarian Danube Flotilla at the Bulgarian port of
Ruse, sinking one barge loaded with fuel and damaging the port's quay. Initially, the only opposing force was the
Austro-Hungarian First Army, which was steadily pushed back toward Hungary. In a short time, the towns of
Brașov,
Făgăraș, and
Miercurea Ciuc were captured, and the outskirts of
Sibiu were reached. In areas populated with Romanians, the Romanian troops were warmly welcomed, and the locals provided them considerable assistance in terms of provisions, billeting and guiding. However, the rapid Romanian advance alarmed the Central Powers, and within weeks sizable reinforcements began arriving at the scene. The Entente incorrectly assumed that Germany would be unable to respond to the invasion, as the
Battle of the Somme and the
Brusilov Offensive were at their height around this time and tied down significant German forces. Nevertheless, eight divisions and an Alpine Corps were deployed under the command of
Erich von Falkenhayn. The Austro-Hungarians also sent four divisions to reinforce their lines, and by the middle of September, the Romanian offensive was halted. A separate Romanian offensive, carried out by the 1st Infantry Division, was much more limited in its aims and it succeeded:
capturing the west bank of the
Cerna River within the
Banat region. The Romanian occupation of the area lasted for over two months, until mid-November. While the Romanian Army was advancing in Transylvania, the first counterattack came from Field Marshal
August von Mackensen in command of a multi-national force composed of the Bulgarian
Third Army, a German brigade and two divisions of the
Ottoman VI Army Corps, whose units began arriving on the
Dobrudja front after the initial battles. This army attacked north from Bulgaria, starting on 1 September. It stayed on the south side of the
Danube river and headed towards
Constanța. Bulgarian troops (aided by the German-Bulgarian Detachment) surrounded and stormed the fortress of
Turtucaia. The Romanian garrison surrendered on 6 September at the conclusion of the
Battle of Turtucaia. At the same time, the Bulgarian Third Army with the 75th Turkish regiment, arrived on the last day of the battle, defeated a Romanian-Russian force including the
First Serbian Volunteer Division at the
Battle of Bazargic, despite the almost double superiority of the Entente. The Romanian Third Army made further attempts to withstand the enemy offensive at
Silistra,
Dobrich,
Amzacea, and
Topraisar, but had to withdraw under the pressure of the enemy forces. Mackensen's success was favoured by the failure of the Allies to fulfill the obligation they had assumed through the military convention, by virtue of which they had to mount an offensive on the Macedonian front and the conditions in which the Russians deployed insufficient troops on the battlefront in the south-east of Romania. These factors meant that the Romanian forces became too strained to put up effective resistance against the enemy advance. Romania had to fight on two 1,600 km-long battlefronts, the longest front in Europe, with a varied configuration and diverse geographical elements (by comparison, the Russian front, stretching from the
Baltic Sea to
Bukovina, was only 1,000 km long). On 15 September the Romanian War Council decided to suspend the Transylvania offensive and concentrate on the Mackensen army group instead. The plan (the so-called
Flămânda Offensive) was to attack the Central Powers forces from the rear by crossing the Danube at
Flămânda, while the front-line Romanian and Russian forces were supposed to launch an offensive southwards towards
Cobadin and
Kurtbunar. Russian reinforcements under General
Andrei Zaionchkovsky arrived to halt Mackensen's army before it cut the rail line that linked Constanța with Bucharest. Fighting was furious, with attacks and counterattacks until 23 September. The Central Powers suffered a tactical defeat in the
First Battle of Cobadin on 19 September, forcing them to halt their advance until mid-October. On 30 September, near the Romanian port of
Sulina, the German submarine
UB-42 launched a torpedo at the Romanian torpedo boat , but missed. The Romanian warship counterattacked, damaging the submarine's periscope and conning tower and forcing her to retreat. On 1 October, two Romanian divisions
crossed the Danube at Flămânda and created a
bridgehead 14 kilometer-wide and 4 kilometer-deep. On the next day, this area was expanded, with 8 Bulgarian settlements ending up in Romanian hands. However, due to the deteriorating situation in Transylvania, the offensive was cancelled on 3 October. The Austro-Hungarian river monitors
Bodrog,
Körös and
Szamos, together with the patrol boat
Barsch and one coal barge were damaged by Romanian coastal batteries and one large barge loaded with explosives was sunk.
Körös took 12 hits and was disabled for the rest of the Romanian Campaign.
The counteroffensive of the Central Powers Overall command was now under
Erich von Falkenhayn (recently replaced as German Chief of Staff), who started his own counterattack on 18 September. The first attack was on the Romanian First Army near the town of
Hațeg; the attack halted the Romanian advance. Eight days later, German troops
attacked Sibiu, and on 29 September, the outnumbered Romanians began retreating to the
Vulcan and
Turnu Roșu passes. The latter, however, had been occupied by Bavarian mountain troops in a flanking movement, and the Battle of Turnu Roșu Pass ended with the Romanians retaking the pass at a cost of 3,000 men. On 17 October the Romanian Second Army attacked the Austro-Hungarians at
Brașov, but the attack was repulsed and the counterattack forced the Romanians to retreat from there also. The
Romanian Fourth Army, in the north of the country, retreated without much pressure from the Austro-Hungarian troops, so that by 25 October the Romanian army was back to its initial positions. The Central Powers succeeded in taking the strategic initiative in Transylvania by concentrating significant military forces rapidly brought in from the other theatres of operations in Europe and exploiting a quick shift of Romanian units to the battlefront in Dobruja. and Hilmi Paşa observing the fighting around
Medgidia -class river monitors (four), Alexandru cel Bun'' minelayer and armed liners Back on the coast, Field Marshal Mackensen and Bulgarian General
Stefan Toshev launched a new offensive on 19 October, after a month of careful preparations, and achieved a decisive victory in the
Second Battle of Cobadin. The Romanians and Russians were forced to withdraw out of
Constanța (occupied by the Central Powers on 22 October). After the fall of
Cernavodă, the defense of the unoccupied Dobruja was left only to the Russians, who were gradually pushed back towards the marshy
Danube Delta. The Russian Army was now both demoralized and nearly out of supplies. Mackensen felt free to secretly pull a large number of troops back to the town of
Svishtov in Bulgaria with an eye towards crossing the Danube river. In mid-November, after several
tactical defeats in the Southern Carpathians (Bran-Câmpulung,
Prahova Valley,
Jiu Valley), Falkenhayn concentrated his best troops (the elite
Alpenkorps) in the south for an attack on the
Vulcan Pass. The
Second Battle of the Jiu Valley was launched on 10 November. One of the young officers was the future Field Marshal
Erwin Rommel. On 11 November, then-Lieutenant Rommel led the
Württemberg Mountain Company in the capture of Mount Lescului. The offensive pushed the Romanian defenders back through the mountains and into the plains by 26 November. There was already snow covering the mountains and soon operations would have to halt for the winter. Advances by other parts of Falkenhayn's
Ninth Army also pushed through the mountains; the Romanian army was being ground down by the constant battle and their supply situation was becoming critical. After conquering the main Romanian sea port of
Constanța during the
Second Battle of Cobadin, the Central Powers set up a naval base which was used by German seaplanes for raids against
Sulina, the last Romanian-held sea port. On 7 November, Romanian anti-aircraft defenses at Sulina (including the old protected cruiser ) shot down into the sea one of the seaplanes, killing the commander of the German squadron. This reduced the German seaplane force at Constanța by a quarter, which only consisted of four aircraft in November 1916. The shot down seaplane was of the
Friedrichshafen FF.33 type, as these were the only German naval bombers on the Romanian front. In total, from 1916 to 1918, German seaplanes serving on the Romanian front were of four types:
Friedrichshafen FF.33,
Hansa-Brandenburg W.12,
Rumpler 6B and
Albatros W.4. In November, the German submarine
UC-15 was sent on a minelaying mission off Sulina and never returned, being sunk by her own mines. This was probably caused by an encounter with the Romanian torpedo boat , whose captain surprised a German submarine near Sulina in November 1916, the latter reportedly never returning to her base at
Varna. This could only be
UC-15, whose systems most likely malfunctioned after being forced to submerge in the shallow waters, upon encountering the Romanian torpedo boat. Her
flotilla briefly remained without a minelaying submarine, until
UC-23 was commissioned in early December. leading his forces across the Danube.
Battles on the Wallachian Plain On 23 November, Mackensen's best troops crossed the Danube at two locations near Svishtov. This attack caught the Romanians by surprise and Mackensen's army was able to advance rapidly towards Bucharest against very weak resistance. Mackensen's attack threatened to cut off half the Romanian army. In response, the Romanian Command prepared a counter-offensive known under the name of the
Battle of the Argeș (part of the
Battle of Bucharest) and designated the recently promoted General
Constantin Prezan to lead it. The plan envisaged the checking of the advance of the German Ninth Army from the north and north-west, as well as the encirclement and annihilation of the German-Bulgarian-Turkish units deployed south-east of Bucharest. It was a bold undertaking, using the entire reserves of the Romanian army, but it needed the cooperation of Russian divisions to contain Mackensen's offensive while the Romanian reserve struck the gap between Mackensen and Falkenhayn. However, the Russian army would not endorse the plan and did not support the attack. On 1 December, the Romanian army went ahead with the offensive along the
Argeș and
Neajlov rivers. Initially, the Romanians experienced success, taking a large number of prisoners, however Mackensen was able to shift forces to deal with the sudden assault and Falkenhayn's forces responded with attacks at every point. Faced with the overwhelming superiority of the invading forces, the Romanian army, its ranks thinned from the previous actions, inferior in equipment and lacking Russian support, failed to check the enemy advance. Although it recorded numerous daring actions (among these the
Prunaru Charge, in which the 2nd
Roșiori Cavalry Regiment was almost wiped out), the Battle of the Argeș ended unfavourably for the Romanian army. The Romanian Second Army made a fighting retreat to the
Siret river, which had originally been fortified against the Russians and was facing the wrong direction, but nevertheless would end up proving invaluable, protected as it was by the impassable Danube Delta to the southeast and a flank in the Carpathians in the northwest. Fierce fighting took place in the Battle of Râmnicu Sărat between 22 and 26 December, with Mackensen's forces entering the town on 27 December. Around this time, the Russians began sending numerous reinforcements to
Moldavia to prevent an invasion of southern Russia. Southern Romania, including
Oltenia,
Muntenia,
Dobruja, and southern Moldavia, was now in the hands of the Central Powers. While retreating, the Romanians burnt stores of grain and destroyed oil wells to prevent them from being used by the Germans. The remaining Russo-Romanian forces in Dobruja abandoned
Măcin on 4 January 1917 and
Brăila on 5 January 1917. Toward the end of the month, extreme frost gave the Bulgarians an opportunity to enter the
Danube Delta. On 23 January, they attempted to cross the marshes at
Tulcea, but suffered heavy casualties to Romanian defenders on the northern bank and stopped. The Romanian Land Forces, supported by the Danube Division of the
Romanian Navy and by the actions of the Romanian cruiser at the mouths of the
Danube, managed to prevent the Central Powers from advancing into the Danube Delta, keeping it under Romanian control until the end of the war. Fighting also ceased in the Carpathian passes, also owing to unfavorable weather. Mackensen's troops were able to capture
Focșani on 8 January, but an attempt to break the
Siret River line on 19 January failed. Thus, the front stabilized and allowed for the Romanian army to be refitted and rebuilt. Romania entered the war at a time of strong crisis for the Entente, drawing upon itself numerous enemy forces, fighting on a very long battlefront and having to change its initial campaign plan permanently. But in spite of the human, material and military efforts made by the Central Powers throughout this period, they failed to achieve their fundamental political and strategic goal to defeat Romania and knock it out of the war. Despite heavy casualties, some 250,000 men (almost one third of the manpower mobilized in August 1916) compared to 105,000 Central Power casualties (including 60,000 Germans), and losses of combat material, the Romanian army was still a force taken into consideration by allies and enemies alike and capable of offering resistance to further attacks. Part of the population moved to the free territory, together with the Romanian government, royal court and public authorities, which relocated to
Iași. Therefore, the Kingdom of Romania continued to exercise the attributes of an independent and sovereign state, allied to the Entente powers. With a view to achieving the unity of action of internal political forces that was indispensable to safeguarding the nation's interests, a government of national union was set up in Iași on 24 December 1916, led by
Ion I. C. Brătianu. The political life in unoccupied territory adopted a fundamental goal to achieve national consensus to find the means to conclude a successful liberation war. Within this framework, debates on some laws envisaging structural transformations (primarily the agrarian reform to re-allocate land to peasants and the introduction of
universal suffrage) responded to popular demands of the citizenry and contributed to the morale of the soldiers in the front lines. The re-organization also involved the other troops (combat engineers, air force, navy) and services, which underwent notable improvements. The directions, organization and methodology of the training of the command staff and the troops were considerably improved and special training centers were set up. Priority was given to
trench warfare, the assimilation of new military technology and night combat. Considerable progress was achieved with the technical-material equipment of the army by means of its provisioning with armament, ammunition and other combat resources from inside the country, but even more importantly from abroad. The Allies supported the maintenance of the Romanian front by continuing to deliver and supplement previously placed orders. In parallel, efforts were made to meet the food and health care needs and special heed was paid to strengthening the soldiers' morale. A notable contribution to the reconstruction of the Romanian army was made by the 1,600-strong
French military mission led by General
Henri Mathias Berthelot, which supervised the process and helped retrain Romanian troops. In early June 1917, the Romanian army's strength grew to about 700,000 men, organized in 207 infantry battalions plus 60 march battalions, 110 cavalry squadrons and 245 artillery batteries, divided among two armies and five corps. The results obtained in terms of re-organization and recovery impressed public opinion both at home and abroad and were to be confirmed in the great battles of the ensuing months. On 16 April, Easter Monday, the Romanian torpedo boat capsized in rough seas off the mouth of the Danube with the loss of 18 of her crew, including 3 French naval officers present on board. This incident has been incorrectly attributed to Ottoman mines in several English language sources, possibly as a result of wartime propaganda by the Central Powers.
1917 campaign and armistice Aware of the complex strategic situation, the Romanian Command lent its military policy a clear, realistic orientation of committing the entire population to battle, trying to act efficiently in keeping with the national goals and in harmony with the large-scale operations worked out at the coalition level. Its final form ready in late May 1917, the operations plan for the Romanian front called for the mounting of a general offensive in the
Focșani-
Nămoloasa sector with a view to completely pin down all enemy forces there, annihilate the main enemy groups operating there (the German Ninth Army) and support the
Kerensky Offensive. The decisive effort was to be made by the Romanian First Army. In order to increase the effect of the offensive and draw as many enemy troops as possible northwest of the town of
Focșani, the actions of the Romanian Second and
Russian Fourth Armies had to precede those of the Romanian First Army. The German High Command, which had moved the center of gravity of its military operations to the Eastern Front in hopes of winning a victory there through the defeat of Romania and the conclusion of a peace with Russia, decided in June 1917 to mount a wide-scope offensive in the north and south of Moldavia, to which end it brought over reinforcements from the other fronts. In early July 1917, on the Romanian front, one of the largest concentrations of combat forces and war material assembled during World War I: nine armies, 80 infantry divisions with 974 battalions, 19 cavalry divisions with 550 squadrons and 923 artillery batteries, whose effectives amounted to some 800,000 men, with about one million in their immediate reserve. The three great battles, decisive for the Romanian nation's destiny, delivered at
Mărăști,
Mărășești and
Oituz, represented a turning point in the war on the Eastern front. These battles were fought approximately on the front alignment stabilized in early 1917, which the conflicting sides had thoroughly consolidated for half a year. during the
Battle of Mărăști The
Battle of Mărăști began on 24 July 1917 at dawn, and took place in
Vrancea County in the sector of the Romanian Second and Russian Fourth Armies. Initiated by surprise with three divisions, the offensive succeeded in disrupting the well-organized enemy defenses and compelling the Austro-Hungarians and Germans to retreat. By the evening, the Romanian divisions had conquered the first defenses, the strongest and deepest of the defensive system of the
Gerok Group of the
Austro-Hungarian First Army in the Mărăști area. The next day, pursuing the offensive, the Romanian troops forced the enemy into an ever more disorderly retreat. This created favorable conditions for a deep penetration into the defensive disposition and the annihilation of the enemy group. However, under the circumstances in which the
Russian High Command decided unilaterally to stall any offensive as a result of the grave situation created on the front in Galicia and Bukovina following the failure of the Kerensky Offensive and the counter-attack of the Central Powers, the Romanian General Headquarters saw itself compelled to discontinue the offensive throughout the entire territory between the Eastern Carpathians and the Black Sea. In the Mărăști zone, however, the Romanian units continued the offensive until 30 July upon the request of their commander, General
Alexandru Averescu. This marked the end of the Battle of Mărăști. It inflicted important losses upon the Austro-Hungarians and Germans, who relinquished a 35 km-wide and 20 km-deep area and sustained heavy casualties and losses in combat resources. The offensive potential of the Romanian army was confirmed through this victory. decorating soldiers at the front For 29 days, until 3 September, this sector was the scene of the most important battle fought by the Romanian army during the 1917 campaign. The
Battle of Mărășești had three distinct stages. During the first stage (6–12 August), the troops of the Romanian First Army, together with Russian forces, managed to arrest the enemy advance and forced the Germans to change the direction of their attack toward the northwest gradually. In the second stage (13–19 August), the Romanian Command completely took over the command of the battle from the Russians. The confrontation reached its climax on 19 August, with the result that enemy's attempts to advance were completely thwarted. The third stage (20 August – 3 September) actually saw the last German attempt at least to improve their positions in view of a new offensive, this one also confounded by the Romanian response. Starting on 8 August 1917, the fighting on the Mărășești front combined with an Austro-Hungarian-German offensive at Oituz. Holding out against superior enemy forces, the Romanian troops by 30 August stemmed the advance of the Gerok Group. The definitive cessation of the general offensive on the Romanian front by the Central Powers on 3 September 1917 marked a strategic defeat and a considerable weakening of their forces on the South-Eastern front. The response of the Romanian army in fact created the strongest blow to the Central Powers that was dealt in Eastern Europe in 1917. The situation, however, once again took a turn for the worse for the Entente in November 1917 with the
October Revolution in Russia and the beginning of
Russian Civil War. These events effectively ended Russian involvement in the war and left Romania isolated and surrounded by the Central Powers. It had little choice but to negotiate the
Focșani Armistice, signed by the combatants on 9 December 1917. ==Aftermath==