HMS Campania was a seaplane tender and aircraft carrier, converted from an elderly ocean liner by the Royal Navy early in the First World War.

Originally built as a passenger liner for Cunard Line's service between Liverpool and New York in 1893, RMS Campania was the holder of the Blue Riband award for speed early in her career.

[1] The Royal Navy purchased Campania from the shipbreakers on 27 November 1914 for £32,500, initially for conversion to an armed merchant cruiser equipped with eight quick-firing 4.7-inch (120 mm) guns.

Her captain recommended that the flying-off deck be lengthened and given a steeper slope to allow gravity to boost the aircraft's acceleration and the ship was accordingly modified at Cammell Laird between November 1915 and early April 1916.

[5] Campania failed to receive the signal to deploy when the Grand Fleet departed Scapa Flow on 30 May 1916 en route to the Battle of Jutland, but she sailed two hours and fifteen minutes later.

Even though she was slowly overtaking the fleet early in the morning of 31 May, she was ordered to return to Scapa Flow as she lacked an escort and German submarines had been reported in the area.

Campania's hull was breached by the initial collision with Royal Oak, flooding her engine room and shutting off all main electrical power.

A Naval Board of Inquiry into the incident held Campania's watch officer largely responsible for her loss, citing specifically the failure to drop a second anchor once the ship started to drift.