HMS Indefatigable was the lead ship of her class of three battlecruisers built for the Royal Navy during the first decade of the 20th Century. When the First World War began, Indefatigable was serving with the 2nd Battlecruiser Squadron (BCS) in the Mediterranean, where she unsuccessfully pursued the battlecruiser Goeben and the light cruiser Breslau of the German Imperial Navy as they fled toward the Ottoman Empire. The ship bombarded Ottoman fortifications defending the Dardanelles on 3 November 1914, then, following a refit in Malta, returned to the United Kingdom in February where she rejoined the 2nd BCS.

The Indefatigable class were the second class built of British battlecruisers which served in the Royal Navy and the Royal Australian Navy during World War I. The design represented a modest reworking of the preceding Invincible class, featuring increased endurance and an improved cross-deck arc of fire for their midships wing turrets achieved by a lengthening of the hull. Like its predecessor, the design resembled the contemporary dreadnought of the Royal Navy, but sacrificed armour protection and one turret from the main battery for a 4-knot speed advantage.