The Goeben was a pretty standard 2nd generation battlecruiser. She was faster, better armoured and better armed than her predecessor, the Von der Tann. She was also generally better than her British counterparts in the Indefatigable-class - the Indefatigables were designed to fight armoured cruisers, while the Moltke class to which Goeben belonged were designed to fight battlecruisers. However, later battlecruisers outclassed her. The British Lion class had similar protection, and outgunned her greatly, while outrunning her. Goeben was, like any other battlecruiser, fast and well armed, but much less armoured than a battleship. She could fight any other cruiser and win, but had limited staying power in a fight against equivalently armed ships.

In August 1914, Goeben and the light cruiser Breslau were operating as the German Navy's Mediterranean Squadron, under the command of Admiral Souchon. War with France was declared while they were en route to Algeria. The two ships bombarded the ports of Philippeville and Bone, before receiving instructions to sail to Istanbul. However, they could not reach Istanbul without refuelling, which they did at Messina, on Sicily. While this refuelling was taking place, Britain declared war on Germany. A squadron of British battlecruisers, under Admiral Milne, had been deployed to keep the ships bottled up in Messina. However, Milne badly misread Souchon's intentions. Believing that Souchon would head west to interfere with French troop convoys to North Africa, he withdrew to cover the convoys. This left Troubridge's 1st Cruiser Squadron, with its four armoured cruisers, as the only large Allied ships in the Eastern Mediterranean. Individually, none of the armoured cruisers was a match for Goeben - it's not clear whether or not four of them could have sunk her together. Shadowed by the light cruiser Gloucester, Souchon's squadron headed East on the 6th August. Troubridge made some attempts to engage, but realised that he wouldn't be able to achieve a favourable position, and withdrew without fighting. Gloucester chased Souchon until he rounded Greece at Cape Matapan, where Troubridge had ordered her captain to disengage. With nothing chasing, Souchon was able to refill his coal bunkers, and steam unhurriedly into Istanbul. The failures of Troubridge and Milne to prevent this led to much upheaval in the Royal Navy. Both officers were effectively removed from command.

To get around neutrality restrictions, the ships were transferred to the Ottoman Navy, though their crews were retained. Goeben was renamed Yavuz, while Breslau became Midilli. Souchon became the commander of the Ottoman Navy. As such, he was able to, on the 29th October 1914, lead a raid on Russian targets in the Black Sea, bringing the Ottoman Empire into the war. Goeben outclassed the obsolete pre-dreadnoughts of the Russian Black Sea Fleet, though could have been threatened by them en-masse. On the 18th November, she fought an inconclusive battle against the Black Sea Fleet, with both sides withdrawing having taken minor damage. Her experience for much of the rest of the war was similar - she bombarded several targets along the Russian coast, and fought several inconclusive engagements. During the Dardanelles Campaign, she attempted to engage the Allied fleet, but swiftly withdrew once she was brought under fire. In 1918, Yavuz and Midilli attacked the base of the Allied fleet blockading the Dardanelles, at Imbros. Two British monitors were sunk, but as the Ottoman ships attempted to attack the naval base at Mudros, they ran onto a minefield. Midilli was sunk, and Yavuz heavily damaged. She withdrew to the Dardanelles, and was grounded on a sandbar until repairs could be carried out. While she was stuck, the RN carried out several air raids against her, though doing little damage due to the light weight of bombs used.

Goeben's main importance to the war was in the fact that without her, the Ottoman Empire might not have entered the war. It's hard to say how this affected the outcome of the war - it certainly devoted a certain proportion of Allied strength, especially in 1915. However, these forces might have been deployed in an equally indecisive adventure elsewhere in the world. The RN had multiple plans for assaults on islands off the German coast, which were dropped in order to carry out the Gallipoli campaign.