Second phase of the Revolutionary war

While the 61st Mechanised and the elite 68th Special Forces brigades were advancing towards Bulgar Rouge territory, NPLA forces established a small fleet of motor boats, which they used to attack Bulgarian cities far away from their reach. The Vidin operation was repeated in Lom, Kozloduy and the nuclear power station on 17 April; Nikopol was under NPLA control by 19 April; Belene, the nearby unfinished nuclear power station and prison were captured on 23 April; Svishtov was captured the day after. On 25 April, NPLA forces captured Batin islet on the Danube, and ceased their offensive in order to consolidate their positions in the settlements they gained. The ranks of the NPLA quickly swelled to 6,500 men, new recruits being introduced both through intimidation and a sense of nationalist revolution.

On 27 April, the two brigades of the Bulgarian military were stationed in Ruzhintsi, Ruzhintsi municipality. The Special Forces brigade was to secure the nearby Gara Oreshets railway station, while 61st brigade was to advance toward Archar on the bank of the Danube, the aim being to cut both supply lines of the NPLA. By 30 April the task was seemingly achieved, but the NPLA used artillery to heavily shell the Army HQ in Ruzhintsi and the Army itself. The military responded with helicopter gunship strikes, but it eventually lost all of its gunships due to their poor condition and NPLA anti-air artillery fire. Army units clashed with NPLA troops in several villages, without much success. Bulgar Rouge forces then proceeded to mount a counterattack by transporting troops along the Danube and launching an attack east of Archar, which eventually ended with the capture of Ruzhintsi by the NPLA and Army units having their supply lines cut.

Despite using heavy equipment, such as IFVs and tanks, the Bulgarian Army proved technologically inadequate to face a full-scale insurgency. Its lack of communications, unmanned aerial vehicles and advanced sensing technology was the cause of numerous casualties in the barren northwestern region. The two brigades suffered massive casualties, and lost several commanders during a one-week battle with the NPLA in several villages. Both Army units collapsed in the face of the much more determined Bulgar Rouge forces, who eventually captured the military's equipment and used its supplies to boost their own forces. A number of Army soldiers deserted and joined the ranks of the NPLA, which served well to replace the fallen combatants and increase its ranks to well over 8,000 men.

With the Bulgarian military having its largest and best-trained units eliminated, the government rushed all available forces against the advancing NPLA, which by mid-May had entered all cities along the Danube and was approaching Varna and Veliko Tarnovo. Hastily organised militia and battalion-sized Army units launched fierce, but incoherent urban offensives in Vratsa to the northwest, Pleven to the north, and Shumen to the northeast. The Army emphasised the capture of Pleven as this would allow to split the NPLA in two. Both the NPLA and the military dug in around or inside the city, and launched massive artillery attacks on each other before any actual infantry advance. On 20 May, NPLA managed to push the militia and Army troops out of Pleven, which was already in ruins.

On 22 May, the military suffered significant casualties after it was ambushed at the Dolni Dubnik oil complex, which was booby-trapped and exploded, killing at least 200 soldiers. By June, Bulgar Rouge forces were holding most of northern Bulgaria, including the TEREM weapons and munitions factories. By the end of the month, their troops were at the gates of Sofia.