During the First World War, Ark Royal participated in the Gallipoli Campaign in early 1915, with her aircraft conducting aerial reconnaissance and observation missions.

Her aircraft later supported British troops on the Macedonian Front in 1916, before she returned to the Dardanelles to act as a depot ship for all the seaplanes operating in the area.

The ship left the area later in the year to support seaplanes conducting anti-submarine patrols over the southern Aegean Sea.

She also supported Royal Air Force (RAF) aircraft in British Somaliland in the campaign against Mohammed Abdullah Hassan in 1920.

She was renamed HMS Pegasus in 1934, freeing the name for the aircraft carrier ordered that year, and continued to serve as a training ship until the beginning of the Second World War in September 1939.

Assigned to the Home Fleet at the beginning of the war, she took on tasks as an aircraft transport, in addition to her training duties, until she was modified to serve as the prototype fighter catapult ship in late 1940.

The Royal Navy had conducted trials in 1913 with a modified cruiser, Hermes, to evaluate the ability of seaplanes to work with the fleet.

[9] Ark Royal carried 500 tonnes (490 long tons) of fuel oil, enough to give her a range of 3,030 nautical miles (5,610 km; 3,490 mi) at 10 knots (19 km/h; 12 mph).

"[11] The ship proved to be too slow to work with the Grand Fleet and for operations in the North Sea in general, so Ark Royal was ordered to the Mediterranean in mid-January 1915 to support the Gallipoli campaign.

A Wight Pusher eventually managed to get into the air and discovered new fortifications down the Straits; it dropped a single 20-pound (9.1 kg) bomb on the Asiatic side of the Dardanelles and returned with seven bullet holes in its skin.

They conducted more aerial reconnaissance and observation missions in support of the fleet later in the month and in early March as it moved further up the Straits.

In preparation for the squadron's arrival, the ship's crew cleared a vineyard on the island to serve as an airfield and unloaded its crated aircraft on 26–27 March.

From 31 March to 7 April, Ark Royal and her companions made several fake landing attempts and her aircraft bombarded the port of Smyrna with little effect.

[13] Ark Royal's aircraft provided support to the Australian and New Zealand troops at Anzac Cove as they landed on 25 April on the Gallipoli Peninsula.

A month later, the battle on the peninsula had bogged down and the success of the German submarine U-21 in sinking two British predreadnoughts forced Ark Royal to move to a safer anchorage at Imbros at the end of May.

Yavuz struck a mine shortly after they exited the mouth of the Dardanelles so they switched targets and sank two British monitors off Imbros Island.

One Baby was quickly shot down and the other was forced to make an emergency landing with engine problems off Imbros; the pilot was able to taxi the aircraft onto a beach and it was recovered several days later.

The ship was withdrawn from the Black Sea in late 1919 and disembarked her seaplanes at Malta to load a dozen Airco DH.9 bombers and 181 personnel of the supporting Z Force for transport to British Somaliland.

The ship arrived in Berbera on 30 December and the squadron was unloaded to support the air and land campaign against Diiriye Guure.

Now equipped with Fairey IIID seaplanes, Ark Royal returned to the Dardanelles until she was transferred back to the United Kingdom late in the year.

The ship was assigned to the Home Fleet when the Second World War began, and was mostly used to train sailors in catapult launching and shipboard recovery techniques.

[24] These fighters were supposed to defend convoys against attacks from Focke-Wulf Fw 200 maritime patrol bombers and to prevent them from radioing location reports to U-boats.

Under the management of the Compania de Navigation Ellanita, the ship sailed from Cardiff to Antwerp in October 1947 to begin conversion to a freighter.