Cornwall briefly blockaded a German cruiser in East Africa in early 1915 before she was sent to participate in the Dardanelles Campaign a month later.

The Monmouths were intended to protect British merchant shipping from fast cruisers like the French Guichen, Châteaurenault or the Dupleix class.

The engines produced a total of 22,000 indicated horsepower (16,000 kW) which was designed to give the ships a maximum speed of 23 knots (43 km/h; 26 mph).

[3] The Monmouth-class ships' main armament consisted of fourteen breech-loading (BL) 6-inch (152 mm) Mk VII guns.

[7] Cornwall, named to commemorate the English county,[8] was laid down at Pembroke Royal Dockyard, Wales, on 11 March 1901,[9] and launched on 29 October 1902, when she was christened by the Countess of St Germans (nominated for this by the local Lord-Lieutenant).

She became a cadet training ship in January 1908 and was assigned to the 4th Cruiser Squadron on the North America and West Indies Station.

[14] En route to the latter, Cornwall captured the German collier SS Syra on 5 August and was transferred to patrol the Brazilian coast in September[12] as part of the 4th Cruiser Squadron under Vice-Admiral Christopher Craddock.

After the German raider Cap Trafalgar was sunk, RMS Carmania was badly damaged, having lost nine men, but was able to rendezvous with Cornwall.

[16] Upon arrival at Port Stanley on 7 December 1914, Sturdee gave permission for Cornwall to put out her fires to clean her boilers and repair one engine.

Vice-Admiral Maximilian von Spee, commander of the German squadron, had other plans and intended to destroy the radio station at Port Stanley on the morning of 8 December.

At 14:45 Glasgow, the fastest of the British cruisers, was close enough to Leipzig to open fire and the two ships exchanged salvos and scoring the occasional hit.

Cornwall closed on the German ship at full speed, trusting to her armour to keep out the 105-millimetre (4.1 in) shells, while the unarmoured Glasgow manoeuvered at a distance.

Leipzig fired two green flares at 20:12 and the British ships closed to within 500 yards (460 m) and lowered boats to rescue the Germans at 20:45.

Cornwall spent much of the rest of the month searching for the German ships that had not yet been captured or destroyed before departing for home on 3 January 1915.

[12] She arrived at Devonport on 11 February 1915 and spent the next month and a half refitting there and in Avonmouth before departing for South Africa on 23 March.

The ship arrived at Kibondo Island off the German East African coast on 27 April to blockade the light cruiser Königsberg in the Rufiji River.

Cornwall resumed patrolling in the East Indies shortly afterwards and continued until Grant hoisted his flag aboard the ship on 22 October as he and his staff was ferried to Hong Kong.

[12] On 16 January 1917, the ship was escorting a convoy of six troopships when she narrowly missed encountering the German commerce raider SMS Wolf off Saldanha Bay.

Cornwall departed Liverpool on 17 August and escorted at least one troopship to Halifax, Nova Scotia, arriving there a week later.