Osowiec Fortress

In September 1914, Russian field defenses surrounding the fortress were attacked by 40 infantry battalions of the German 8th Army; the attackers enjoyed significant numerical superiority. By 21st of September, the German advance brought the fortress proper within range of German artillery; further reinforced with 60 additional guns of calibers up to 203mm, but these could only be brought into action on 26 September. Two days later, a German frontal assault was repelled by Russian artillery. The day afterwards, two Russian flanking counter-attacks forced German artillery to relocate, taking the fortress outside of German artillery range.

On 3 February 1915, the numerically superior Germans launched another assault. The first line of Russian field defenses consisted of shallow trenches and held for five days. On 9 February the Russians withdrew to the second line with deep trenches and established machine gun emplacements, and gave no ground for another two days. The second line remained unbroken.

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 from 100 mm up to 420 mm, firing in salvos of 360 guns every four minutes. Throughout the week-long artillery barrage, 250,000 shots were fired from the heavy guns and about one million rounds were fired from the light artillery pieces.

Russian Central Command expected the fortress to fall; it requested the defenders to hold for at least 48 hours to allow for evacuation of civilians. The fortress would hold until August.

The Russians suffered heavy losses from the artillery barrage, which was strongest from 14 to 16 February and from 25 February to 5 March 1915. Multiple hits inside the fortress and the collapse of many buildings made movement between different parts of the fortress almost impossible. Subsequently, the sector relapsed to positional warfare.

It is sometimes incorrectly claimed that Russian counter-battery fire destroyed two German heavy mortars; these guns were withdrawn for operations elsewhere.[2]

Lieutenant Vladimir Karpovich Kotlinsky, commandant of the Osowiec fortress during the attack

The Germans launched a full frontal offensive on the fortress at the beginning of July; the attack included 14 battalions of infantry, one battalion of sappers, 24–30 heavy siege guns, and 30 batteries of artillery equipped with poison gases led by Field Marshal Paul von Hindenburg. Russian defenses were manned by 500 soldiers of the 226th Infantry Regiment Zemlyansky, and 400 militia.

The Germans knew the Russians did not have any gas masks so the chose to use chlorine gas. The Germans waited until 4 a.m. on 6 August for favorable wind conditions, when the attack opened with regular artillery bombardment combined with chlorine gas.[3] The ensuing battle was known as the Attack of the Dead Men. The Russians put on wet rags on their faces to filter some of the gas. Most died but some survived the gas attack. Even while suffering severe chemical burns the Russians were able repel the attack because the Germans panicked and retreated.

The Russians did not hold Osowiec for much longer. The Germans threatened to encircle the fortress with the capture of Kovno and Novogeorgiesk. The Russians demolished much of Osowiec and withdrew on 18 August.[2][4]