Osowiec Fortress (Polish Twierdza Osowiec) - Is a 19th-century fortress located in north-eastern Poland, originally built by the Russian Empire. The Russian name is Крепость Осовец i.e., Krepost Osovets. In English sources it is variously given as Osowiec, Osovets, Ossovetz, Osovetz and Ossovets. It saw heavy fighting during World War I when it was obstinately defended for several months by its Russian garrison against German attacks.
The fortress was built in the years 1882-1892 as one of the defensive works to protect the western borders of Russia against Germany, and continuously modernised afterwards to cope with advances in heavy siege artillery. In 1889-1893, military engineer Nestor Buinitsky took an important part in the creation of the fortress. It was located on the river Biebrza about 50 km from the border with the German province of East Prussia, in the one place where the marshlands of the river could be crossed, hence controlling a vital chokepoint. The extensive marshlands and bogs that surrounded it made attack difficult. The strategic Białystok - Ełk (Lyck) - Königsberg (Kaliningrad) rail line ran through the fortress and crossed the Biebrza river there. The fortress saw heavy fighting during the beginning of World War I in the eastern front from September 1914 until the Russian Army abandoned it in August 1915. In the interwar years the fortress was used by the Polish Army. During the German invasion of Poland in 1939 it was bypassed and did not see much fighting.
Today, some parts of the fortress are accessible to tourists, especially the parts within the boundaries of Biebrza National Park. The visitor information center of the park is located in Osowiec-Twierdza, a small settlement located within the boundaries of the fortress. Other parts of the fortress still belong to the Polish Army and access is restricted.
1st German Assault - September 1914
In September 1914 the fortress was put under siege by parts of 8th German army - 40 infantry battalions that attacked straight from their marching order. By 21 September, having huge advantage in numbers, Germans troops were able to push back Russian field defenses to the point where the artillery could fire upon the fortress itself. At the same time German command has added reinforcements of 60 artillery pieces of caliber up to 203mm. But those pieces could only start firing on 26 September 1914. In two days the Germans decided to try frontal assault of the fortress, but it was cut down by a fierce fire from Russian artillery. Next day Russians made two flanking counter-attacks that forced Germans to quickly relocate artillery to a safer place, but they were no longer able to fire upon the fortress.
2nd German Assault - February- March 1915
On 3 February 1915, German forces attempted 2nd assault on the fortress. A long and hard battle was fought for the control of 1st line of field defenses. The Russian forces were able to hold off numerically superior forces for 5 days in shallow trenches. Only on 9 February Russian command decided to pull back all the forces to the 2nd field defense line that had deep trenches and established machine gun placements.
During next two days Russian forces gave no ground, but the retreat from the first line allowed German artillery to start firing on the forts on February 13. The caliber of German heavy siege artillery varied form 100 to 420 mm. The cannons fired in groups of 360, every four minutes 360 explosions rattled the fortress. During the week of intense artillery barrage 250,000 shot were fired by just the heavy guns and about one million of light artillery rounds. Also specifically for this siege the Germans transferred four heavy mortars of 305 mm caliber from France and also transferred a couple of bomber squadrons.
The Russian Central Command, thinking that they were asking the impossible, asked the fortress to last at least 48 hours so evacuation of civilians can be completed. The Osowiec Fortress lasted for half a year.
The Russian side suffered heavy losses from the artillery barrage that was the strongest from 14 to 16 February and from 25 February to 5 March 1915. Multiple fires inside the fortress and collapse of many buildings made movement between the parts of the fortress almost impossible. Even in those hellish conditions Russian artillery managed to destroy two out of four heavy mortars (Big Bertha) and forced German command to pull the remaining two back.
Because 2nd Russian field defense line was never breached Germans were forced into positional warfare on this part of the front until beginning of July.
3rd German Assault
At the beginning of July under the command of field-marshal von Hindenburg German forces began a full frontal offensive on the fortress. Forces included- 14 battalions of infantry, one battalion of sappers, 24-30 heavy siege guns, 30 batteries of poison gases. The Russian side had 500 soldiers of 226 Earth division and 400 militia men.
Germans waited until 6 August for the right wind conditions. At 4 am, at the same times as regular artillery started firing, German forces used poison gases against the defenders. Thinking that all of the defenders were dead, Germans started advancing. Fourteen battalions of Landwehr - at least 7000 infantry men - were participating in that attack. When German infantry reached the first line of defense, they were counter-attacked by what was left of 13-th company of the 226-th Zemlyansk regiment (about 60 men). Surprise attack and bloody clothing (Russian soldiers were coughing blood up because of poison gases destroying the lung tissue) put Germans in the state of shock and made them run. The five remaining Russian guns opened fire at this point aiming at the running mass of Germans. European papers called it "The attack of the dead men"
Fifteen days later, the Russian command finally pulled back the last remaining soldiers from Osowiec and retreated to new positions.
- Хмельков С. А. (Khmelkov, S.A.) (1939). Борьба за Осовец (Struggle for Osovets) (in Russian). Moscow: Государственное военное издательство наркомата обороны СССР.
- Perzyk Bogusław (2004). Twierdza Osowiec 1882 - 1915 (in Polish). Warszawa: Militaria Bogusława Perzyka. ISBN 83-907405-1-6.