In September 1939, 182 km of the Soviet frontier long the river Western Bug were safeguarded by a series of border outposts of the 17th Border Guards Detachment. In 1940, the construction of the 62nd Brest Fortified Sector started along the frontier.
On the eve of the war-outbreak the majority of the Soviet military units was away from the fortress at the construction of the Brest Fortified Sector or at summer training camps.
Within the Brest Fortress some units of the Soviet 6th and 42nd Infantry Divisions, various smaller units (including regimental training units, some divisional artillery units, the garrison hospital etc) to talled about 7-8 thousand people. About 300 officers’ families lived in the fortress.
By the end of June 21, 1941, the German High Command concentrated its powerful strike forces along the USSR border. For the assault of Brest, the 12th Army Corps of the Wehrmacht 4th Army was deployed. It was the Wehrmacht 45th Infantry Division that was supposed to assault the Brest Fortress directly. The task of the division was set in the following order. The assault groups of the 130th and 135th Infantry Regiments were to launch an attack to surround the fortress, eliminate the Soviet military units inside and occupy the territory of Brest, as well as the railway bridges and walkways over the rivers Bug and Mukhavets. Advancing the break-in assault of the fortress, the division was to spearhead further eastwards. For the preparatory surprise bombardment on the Brest Fortress, all divisional artillery was built up, including two largest 600-mm self-propelled siege mortars nicknamed «Karl» shooting concrete piercing shells, weighing 2.2 tons each.
The chaplainof the 45th Infantry Division Rudolf Gschöpf recalledin his book «Mein Weg mit der 45. Infanterie-Division»: «…at 03.15 am, a hurricane broke out and roared over our heads to a degree, that neither before nor during the war we ever experienced».
The 28th Rifle Corps commander, Major-General V.S.Popov reported as follows: «...On June 22, 1941 4.15 am, the enemy from close distances unexpectedly opened a focused brief artillery fire (at least 4-5 artillery regiments) at the districts - the fortress, the Northern and the Southern military quarters in the town... In the first period of shelling the bridges were destroyed, cutting the way out of the fortress (across a branch of the Mukhavets River). Buildings and warehouses within the fortress, the military quarters and the area around the Brest railway station caught fire quite soon. The continuing intensive bombardment made the fire rapidly spread around.
Any communication link was cut off at once. In these circumstances, part of the Brest garrison began the movement, required on alert, suffering heavy losses in personnel and munitions. The assembly and re-deployment of units of the corps, to be done in the event of high alert, were thwarted ... Theartillery shelling and the raging fire split the garrison into separate groups. Some of them were searching for shelter to hide from the shelling, the others were making their way to the exits from the fortress, passing through the fire and incessant explosions of shells. Eventually, we managed to withdraw some disparate units of the 333rd and 125th Rifle Regiments, and a separate group of 44th, 455th and 84th Rifle Regiments.
To sum up, some part of the garrison suffered losses in killed, wounded and missing. The warehouses and most of garrison’s munitions were destroyed. The overwhelming majority of officers’ families remained in Brest and within the fortress. In total, 50% of the units, stationed in the fortress, were withdrawn...»
Taking into account the losses in killed and wounded during the opening hours of the war, it can be assumed that not more than 3.5-4 thousand soldiers and officers were defending the fortress.