She damaged the German battlecruisers Seydlitz and Derfflinger during the Battle of Jutland in mid-1916 and watched her sister ship HMS Invincible explode.

[6] At full fuel capacity, she could steam for 3,090 nautical miles (5,720 km; 3,560 mi) at a speed of 10 knots (19 km/h; 12 mph).

[9] Her anti-aircraft armament consisted of a single QF 3 inch 20 cwt AA gun on a high-angle MKII mount at the aft end of the superstructure that was carried from July 1915.

[10] After the Battle of Jutland revealed her vulnerability to plunging shellfire, additional armour was added in the area of the magazines and to the turret roofs.

[13] Immediately after commissioning, Indomitable embarked the Prince of Wales (soon to be King George V) for the City of Quebec Tercentenary celebration.

She was refitted several times between 1910 and 1913 before she was transferred to the Mediterranean on 27 August 1913 to form the 2nd Battlecruiser Squadron (BCS) with her sister ship Invincible.

[15] Indomitable, accompanied by HMS Indefatigable, under the command of Admiral Sir Archibald Berkeley Milne encountered the German battlecruiser Goeben and the light cruiser Breslau on the morning of 4 August 1914 headed east after a cursory bombardment of the French Algerian port of Philippeville, but Britain and Germany were not yet at war so Milne turned to shadow the Germans as they headed back to Messina to recoal.

Therefore, Milne stationed Inflexible and Indefatigable at the northern exit of the Strait of Messina, still expecting the Germans to break out to the west where they could attack French troop transports, the light cruiser Gloucester at the southern exit and sent Indomitable to recoal at Bizerte where she was better positioned to react to a German sortie into the Western Mediterranean.

Milne, still expecting Rear Admiral Wilhelm Souchon to turn west, kept the battlecruisers at Malta until shortly after midnight on 8 August when he set sail for Cape Matapan at a leisurely 12 knots (22 km/h), where Goeben had been spotted eight hours earlier.

Finally on 9 August Milne was given clear orders to "chase Goeben which had passed Cape Matapan on the 7th steering north-east."

Milne still did not believe that Souchon was heading for the Dardanelles, and so he resolved to guard the exit from the Aegean, unaware that the Goeben did not intend to come out.

In a twenty-minute bombardment, a single shell struck the magazine of the fort at Sedd el Bahr at the tip of the Gallipoli peninsula, displacing (but not destroying) 10 guns and killing 86 Turkish soldiers.

[19] This attack actually took place before a formal declaration of war had been made by Britain against the Ottoman Empire which didn't happen until the 5th.

By 10:48 Blücher had been heavily damaged by fire from all the other battlecruisers and her speed had dropped to 17 knots (31 km/h; 20 mph) and her steering gear had been jammed; Beatty ordered Indomitable to attack her.

[13] After the end of the battle Indomitable was ordered to tow Lion back to port as one of her engines had been knocked out, the other was failing and she'd been holed a number of times beneath the waterline.

Hood interpreted this as an attempt to escape through the Skagerrak and ordered an increase in speed to 22 knots (41 km/h; 25 mph) at 15:11 and steered East-Southeast to cut off the fleeing ships.

The German ships turned for the south after fruitlessly firing torpedoes at 18:00 and attempted to find shelter in the mist.

The 2nd Scouting Group was escorted by the light cruiser Regensburg and 31 destroyers of the 2nd and 9th Flotillas and the 12th Half-Flotilla which attacked the 3rd BCS in succession.

As Invincible turned north, her helm jammed and she had to come to a stop to fix the problem, but this was quickly done and the squadron reformed heading west.

A 305 mm (12-inch) shell from the third salvo struck the roof of Invincible's midships 'Q' turret, flash detonated the magazines below, and the ship blew up and broke in two, killing all but 6 of her crew of 1,032 officers and men, including Rear-Admiral Hood.

Seydlitz was hit five times before the German battlecruisers were rescued by the appearance of the pre-dreadnought battleships of Rear Admiral Mauve and the British shifted fire to the new threat.

[31] The loss of three battlecruisers at Jutland (the others were Queen Mary and Indefatigable) led to the force being reorganised into two squadrons, with Inflexible and Indomitable in the 2nd BCS.

However, after Jutland there was little significant naval activity for the Invincibles, other than routine patrolling, thanks to the Kaiser's order that his ships should not be allowed to go to sea unless assured of victory.