On the Eastern front, the Germans found themselves facing masses of hundreds of thousands of enemy troops. True, Field Marshall Hindenburg (with the close assistance of Ludendorf and Hoffmann) had proven that he could defeat the Russians handily, it would take time to bloody the Russians to such a degree as to force their withdrawal from the war.
So the Germans sought out other means of quickly dispensing with the Russians, and on January 31, at the Battle of Bolimov (a part of the Second Battle of the Masurian Lakes), they used poison gas for the first time in First World War.
It was an unconditional failure: the wind switched directions shortly after its release, often blowing the gas right back towards the Germans, and at any rate, the cold temperatures generally prevented the gas from vaporizing.
Poison gas would make a re-entrance later in the year, with more notable results at Ypres.
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As another part of the German understanding that they had to win and try to win as quickly as possible, they unleashed their submarines, allowing the boats’ commanders fire, without warning, on any ship flying the flag of one of their enemies.
While we in modernity, who are aware of stealth drones being able to eliminate anyone on earth in the blink of eye, don’t really bat an eye at the idea of “unrestricted submarine warfare,” the idea made many people of 1915 blanch in horror: seamen were supposed to have warning, at least a shot across the bow and an opportunity to surrender their ship.
The world, however, was still adjusting to the emergence of the submarine: a slow and fragile seacraft, submarines of WWI had the advantage of stealth, but little else. In a large sense, submarines faced the choice of a sneak attack, or none at all.
Finally, we may look back at these innovations and curse Germany, but the reality is that the Allies were just as guilty of “dirty” tactics and strategies in war. Indeed, it would not take long before the they themselves began to employ chemical weapons, and one could make an argument that Britain herself had provoked Germany’s policy of unrestricted submarine warfare: by enforcing a blockade of Germany with her surface warships, Britain shifted the emphasis of the war very clearly into a conflict of attrition, rather than as a contest of military forces. Germany had little choice but to retaliate in the only way she could: an attempted blockade of Britian, using the only ships that could evade the British blockade, submarines.