The World War I era takes place entirely in Eastern Prussia, during the opening stages of the war on the Eastern Front between Germany and Russia. In the fall of 1914, a nigh month after Germany pledged that it would support Austria-Hungary in the war, the Russians launched an attack into Germany to support its ally, Serbia. This attack, dubbed the Battle of Tannenberg (of which the entire World War I segment revolves around), consisted of the First and Second Russian armies, totalling about 400,000 men. The smaller German Eigth Army skillfully outmaneuvered and destroyed the Russians, and handed them a staggering defeat that they would not recover from for years. For reasons unknown, the Russian commanders broadcasted their marching orders unencoded over open radio, which were intercepted at liesure by the Germans.
The First World War is characterized and renowned for its mass use of defensive trench warfare, human wave attacks, and static machine gun nests. The nature of the game allows this to all be represented very believably, and for the most part, accurately. The technology of the period has not yet reached the advent of portable semi-automatic or automatic weapons - as such, most weapons with exception of pistols are heavy calibre bolt-action, requiring manual operation of the bolt to load the next round to fire. Static machine gun positions dominate the battlefield, and much focus is put into artillery bombardments to achieve breakthroughs, deforming the forests and fields into nightmarish landscapes.
The Russian Second Army is left out to dry and is summarily encircled and destroyed. Somehow a particularly important person, Captain Petrovich, has been shifted to the Second Army. This is not according to conventional history, and thus the player, Alexander Morris, is sent into the thick of battle near Allenstein to try and locate Petrovich. Upon his arrival, the Germans are making heavy attacks on the encircled 2nd army, and the player uses a Maxim MG08 machine-gun to surpress attacking Germans and allow Petrovich to fall back out of danger, as he is found pinned in no man's land. After being saved, he runs far behind the line to safety where Morris and Dexter are unable to locate him, and so they shortly after return to the Kronotek lab to plan a new mission to return and retrieve him later.
The Russians take heavy losses near Allenstein and fall back to the Frankenau line, where they've set up a heavy defensive position. Alexander Morris is dropped south of it, and fights his way through masses of German patrols and scattered battles to make his way to the Russian line. Shortly thereafter, the Germans make a human wave attack on the line and are repulsed with the aid of Morris in the trenches, and then with his use of the experimental MA22 Artillery.
Petrovich however, has still managed to elude Dexter and the Player. Another excursion is made to a wooded region near Frankenau where a battle is supposed to be taking place. Following Dexter and the player are two undercover Kronotek agents dressed as Russians. It quickly becomes apparent that things have gone awry, as Germans have taken up positions in places where they shouldn't be, the Russians are nowhere to be found, and a heavily guarded Zeppelin is near their entry zone. Despite his orders, and his mission to not alter the time-stream, Dexter decides to commandeer the Zeppelin and fly out to help the Russians in the battle and locate Petrovich.
The player then must use the Zeppelin's mounted MG08's, a strangely provided Gewehr 98k sniper rifle, and handheld bombs to fend off the Germans from destroying the Zeppelin. After fighting past a large artillery position, The Zeppelin stumbles upon Petrovich in the back of a truck being pursued by a German truck filled with riflemen. After the player uses his rifle to shoot the Germans out of the bed of the truck, the Zeppelin takes heavy damage from the mortars and begins to go down. However, Dexter manages to warp them back to Kronotek before it impacts the ground. Unfortunately the two agents are left behind, presumably to die.
After Dexter explains what happened to Mother, it's revealed that Morris's overzealous use of the MA22 caused both the Russians and the Germans to flee in fear. Dexter and Morris are sent in to stir things up a bit by attacking German positions, and giving the Russians the edge they need to blow up the Trestle bridge.
- Although the World War I battlefields are re-created to plausible effect, it should be noted that the doctrine of defensive trench warfare didn't take hold until 1915. Early 1914, and especially on the large open terrain of the Eastern Front, didn't feature such deep planned out fortified positions and was largely manuever warfare - what allowed the Russians to be encircled at Tannenberg in the first place.
- Russian Maxim guns are absent from the battlefield. For some reason even Russian trenches use the German MG08 Machine-guns.