After the battle of Marasti ended, the 2nd Army occupied the following positions: the 4th Corps had the 7th Infantry Division between the Dofteana and Oituz Rivers, the 6th Infantry Division between the Oituz River and the Casin Hill and the line was continued to the north to the Zboina Neagra by the 8th Infantry Division. The 2nd Corps had between the Zboina Neagra and Sarii Valley the 12th, 1st and 3rd Infantry Divisions. Four battalions made up the reserve. There hadn't been enough time to strengthen the weak fortifications existing in the area.
On the other side, teh Austro-Hungarian 1st Army planned to attack with its left wing, the Gerock Group, along the Oituz Valley. The main strike element was the Austro-Hungarian 8th Corps, deployed between the Dofteana Valley and the Casin Hill, in front of the Romanian 7th and 6th Infantry Divisions. It was made up of the Austro-Hungarian 70th and 71st Infantry Divisions and the German 117th Infantry Division. In reserve it had the Austro-Hungarian 7th and 8th Cavalry Divisions, which were ready to exploit the eventual break through of the infantry.
The attack was supposed to start on 8 August 1917. The German 117th Infantry Division had to advance north of the Oituz Valley, towards the Ungureanu and Cosna Peaks and the Austro-Hungarian 71st Infantry Division had to advance south of the valley. The 70th Division was going to attack towards Targul Ocna over the Ciresoaia and Pravila Peaks. The front was 7 km wide and the Central Powers had a 4 to 1 numerical superiority.
The artillery preparation lasted four and a half hours and was extremely violent. In the sector of the 7th Infantry Division, the Pravila Peak was assaulted four times by the Austro-Hungarian 70th Division, but the 27th Dorobanti Regiment Bacau, on the right wing of the Romanian division, stood its ground. On the left wing, the 16th Dorobanti Regiment Baia was hard pressed by the German 117th Division and gave away 1-2 km in the area around Ungureanu Peak, suffering high casualties. The 9th and 10th Companies were surrounded, but managed to break through to the friendly lines. The Balcuta Peak was attacked by the Austro-Hungarian 71st Division, which, with great effort, pushed 1-2 km back the 11th Dorobanti and 7th Vanatori Regiments. To the south, the 10th Dorobanti Regiment Putna kept its position. Thus, during the first day of the battle, the Austro-Hungarian 8th Corps made a break through in the central part of the front.
During the night, general Valeanu, the CO of the Romanian 4th Corps, ordered a counterattack in that area. His troops managed to regain some of the ground lost during the day. The 27th Regiment captured 200 prisoners, 3 machine-guns and a gun. But on 9 August, in the afternoon, the Central Powers resumed the offensive. The German 117th Infantry Division forced the 16th Regiment to abandon the Cosna Mountain. The Austro-Hungarian 70th Infantry and 7th Cavalry Divisions took the Pravila Peak. The Romanian 7th Infantry Division retreated to a new line of defense.
On 10 August 1917, the pressure on the 7th Division increased, the Romanian troops having to abandon Slanic. The remaining positions on the Cosna Mountain were repeatedly assaulted, but resisted. For the Romanians the situation was critical, because the troops in the first line were exhausted after three days of very violent fights and the reserves of the 4th Corps were inexistent. Also, the current positions were situated on the last heights standing in front of the Trotus Valley and the road to the plains beyond. Lt. general Alexandru Averescu, the CO of the 2nd Army, ordered the 2nd Corps to urgently send all its available reserves and asked for more troops from the Romanian General Headquarters. Because in the same time, the 1st Army was engaged into a more violent clash at Marasesti with the German 9th Army, all that could be sent was the 1st Cavalry Division, which arrived at Onesti the following morning. The Mountain Battalion (the first such unit in the Romanian army) and the Frontier-guard Brigade were on their way to Oituz.
General Gerock, seeking to achieve the much desired break through into the Trotus Valley, engaged his last reserves in the battle on 11 August. The 70th Infantry and 7th Cavalry Divisions attacked the Ciresoaia Peak, defended by the 15th Dorobanti Regiment Razboieni. All assaults were repulsed, but several Austrian units infiltrqated south of the peak and the Romanian regiment had to retreat in the Trotus Valley to avoid encirclement. Targul Ocna was directly threatened. To the south, the German 117th Division again assaulted the Cosna Mountain, but failed. However, several advances were made south of the mountain, which were stopped in the Oituz village. With their rear threatened, the Romanian troops on Cosna pulled back. The Gerock Group had managed to conquer the last two heights separating it from the Trotus Valley. At this moment the Romanian reinforcements had arrived. Two battalions attacked in the Ciresoaia area and managed to regain some of the lost ground and create the link with the Russian 9th Army. At 1900 hours the 1st Cavalry Division was also thrown into battle. It attacked with one brigade the German troops on the southern slope of the Cosna Mountain and with the 2nd Rosiori Brigade the Stibor Hill and by nightfall it had secured both objectives. The 1st Vanatori Regiment, sent by the 2nd Corps, counterattacked in the Oituz village supported by two armored cars and repulsed the units of the 117th Division.
The danger had passed, but the advance of the German 18th Reserve Corps in the Panciu area, on the 2nd Army's left flank forced general Averescu to move a part of the reserves to the 2nd Corps. Even though its forces had decreased and the Frontier-guard Brigade had arrived yet, general Valeanu decided to retake the Ciresoaia Peak on 12 August. The attack was carried out by the 27th Dorobanti Regiment, a battalion of the 15th Regiment, two battalions from the Russian 2nd Division (from the 9th Army) and the Mountain Battalion (which was in fact a strengthened battalion, made up of 5 rifle and 2 machine-gun companies). The latter had just arrived following a 160 km march and started the attack after a 20-minute pause. To achieve surprise, there was no artillery preparation. The Mountain Battalion, commanded by maj. Virgil Badulescu, broke through the defense of the Austro-Hungarian 70th Division and infiltrated befind enemy lines. It captured 417 prisoners and 4 machine-guns, while suffering minimal casualties: 2 dead and 19 wounded. In total the Austro-Hungarian division lost 1,500 men at Ciresoaia. For this action, the commander and seven of the battalion's officers received the Mihai Viteazul Order 3rd class, approximately a third of the 25 awarded for the actions during the battle of Oituz. The battalion's flag was also decorated this prestigious award.
During the night the Frontier-guard Brigade had arrived. It received the task to attack south of the Oituz River. The 1st Cavalry Division, strengthened with four battalions and two batteries had to retake the Cosna Mountain and advance on Slanic, while the 7th Infantry Division had to continue the advance in the Ciresoaia area.
On 13 August, at 0500 hours, after a short artillery preparation, the 7th Division started the attack together with the Russian 2nd Division on its right, forcing the Austro-Hungarian 70th Division to retreat. The Gerock Group sent the reserves, which repulsed the Russian 195th Infantry Regiment, threatening the flank of the Romanian troops, which had to also pull back. In the Cosna sector, the 1st Cavalry Division managed to take the peak an hold it in front of the counterattacks of the German 117th Infantry Division. The Frontier-guard Brigade, commanded by colonel Gheorghe Cantacuzino, who had been awarded the Mihai Viteazul Order 3rd class for the fights in 1916, was tired following the march in the previous days. He asked for a postponement. The attack started at 1000 hours, but failed because of the stiff resistance put up by the Austro-Hungarian 71st Division. In the afternoon, a second assault had the same fate. The losses were estimated at about 800 men.
A pause of five days followed. There were local clashes and the two sides reorganized their forces and entrenched their positions. On 16 August, the 2nd Frontier-guard Regiment took the Runcu Peak, two of its offices being awarded the Mihai Viteazul Order 3rd class for this action.
On 19 August, the Austro-Hungarian 1st Army resumed the offensive. The sector chosen for the attack was the Cosna Peak, defended by the 1st Cavalry Division, which had been introduced between the 6th and 7th Infantry Divisions. Wisely using their numerical superiority, the Germans managed to take the peak, but the Romanian cavalrymen retreated to the mountain's eastern slope, where they resisted the following assaults. During the night, the 2nd Army sent two frontier-guard battalions and an infantry regiment as reinforcements. On 20 August, at 0700 hours, the strengthened 1st Cavalry Division, supported by the entire Romanian artillery available in the area, attacked and managed to regain some of the ground lost the previous day.
This action was the last major episode of the second battle of Oituz, carried out in the summer of 1917. The Austro-Hungarian 1st Army had managed to advance only 2-6 km deep on a 20 km wide front and failed to break through into the Trotus Valley and from there to threaten the rear of the Romanian and Russian armies in southern Moldavia. In total, 25 Mihai Viteazul Orders 3rd class were awarded to the Romanian officers for the actions in August 1917 in the Oituz area. The battle flags of only three units (one regiment and two battalions) also received the prestigious award.