During the First World War, she participated in the Battle of Heligoland Bight in a minor role, as she was the oldest and slowest of the British battlecruisers present.

[2] Invincible had two paired sets of Parsons turbines, each of which was housed in a separate engine-room and drove an outboard and inboard shaft.

The situation was so bad during her gunnery trials in October 1908 that the captain of HMS Excellent, the Royal Navy's chief gunnery school, described their operation in the following manner: "When the order was given to train the turret, elevate or run a gun in or out, it was only necessary to push a button, or move a switch, but the result was often a flash of blue flame which seemed to fill the turret.

[10] 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 between October–November 1914 and from April 1915 onwards.

[12] On 28 December 1907, while still fitting out, she was hit by the Swedish collier Oden, which resulted in the buckling of beams and frames in the hull and five bottom plates being stove in.

She returned to the UK in December 1913 in preparation for a major refit that would finally give her turrets hydraulic power and make her battle-worthy.

Invincible was the first battlecruiser to be fitted with a new fire-control director, but this could not be completed in the allotted time and would remain inoperable until she was refitted after the Battle of the Falkland Islands.

[17] She was declared operational on 12 August, when Rear-Admiral Sir Archibald Gordon Moore, commanding the 2nd Battlecruiser Squadron, hoisted his flag in her.

[18] Invincible's first action was as part of the battlecruiser force under the command of Admiral Beatty during the Battle of Heligoland Bight operation on 28 August 1914.

They turned south at full speed at 11:35[Note 1] when the British light forces failed to disengage on schedule and the rising tide meant that German capital ships would be able to clear the bar at the mouth of the Jade estuary.

Beatty was distracted from the task of finishing her off by the sudden appearance of the elderly light cruiser Ariadne directly to his front.

She fired 18 rounds, all misses,[20] before Beatty's main body encountered the crippled Cöln shortly after turning north and she was sunk by two salvos from Lion.

They departed on 11 November and rendezvoused with several other cruisers under Rear Admiral Stoddard at Abrolhos Rocks, off the coast of Brazil on the 26th.

They were spotted at 07:30, although the pre-dreadnought Canopus, grounded in Stanley Harbour to defend the town and its wireless station, did not receive the signal until 07:45.

The German ships were not expecting resistance and the first salvo from Canopus's guns at 09:20 caused them to sheer off from their bombardment of the wireless station and fall back on Spee's main body.

The light cruiser Leipzig lagged behind the other ships and Inflexible opened fire when the range dropped to 17,500 yards (16,000 m) at 12:55.

Invincible opened fire shortly afterward and both ships began straddling Leipzig as the range closed to 13,000 yards (12,000 m).

The German ships opened fire at 13:30 and scored their first hit at 13:44 when Scharnhorst struck Invincible, though the shell burst harmlessly on the belt armour.

Both sides fired rapidly during the first half-hour of the engagement, before Sturdee opened up the distance to put his ships outside the effective range of the German guns.

[24] Spee turned to the south in an attempt to disengage while the British had their vision obscured, but only opened the range to 17,000 yards (16,000 m) before his course change was spotted.

Spee turned to the northwest, as if to attempt to cross the British T, but actually to bring Scharnhorst's undamaged starboard guns to bear as most of those on his port side were now out of action.

Gneisenau had been slowed by earlier damage and was battered for another hour and a half by Inflexible and Invincible at ranges down to 4,000 yards (3,700 m).

This took a month, and the opportunity was taken to extend the height of her fore funnel by 15 feet (4.6 m) to reduce the amount of smoke blocking visibility from the bridge and spotting top.

Invincible's speed was reduced to 12 knots (22 km/h; 14 mph) through flooding and she was forced to haul out of line and proceed independently to Rosyth for repairs which lasted until 22 May 1916.

Hood interpreted this as an attempt to escape through the Skagerrak and ordered an increase in speed to 22 kn (41 km/h) 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.

Examination of the wreck has found that the 12 inch guns in the aft turret remain loaded although its roof is missing.

Coupled with the aft turret's missing roof, it implies that 'X' magazine also caused a low-order explosion within the ship.