At the outbreak of the First World War eight German cruisers were outside home waters or the Mediterranean. The five ships of Vize Admiral Maximilian Spee’s East Asia Squadron sank the British armoured cruisers HMS Good Hope and Monmouth at the Battle of Coronel on 1 November 1914, but four of them were then sunk at the Falklands on 8 December. The other, SMS Dresden, was destroyed on 14 March 1915. These ships sank or captured a total of 29,826 tons of Allied merchant shipping, 12,927 of it by Dresden and 15,299 by SMS Leipizig.
The two most successful German commerce raiders in the early stages of the war were SMS Emden, which accounted for 82,938 tons of merchant shipping, the Russian cruiser Zhemchug and the French destroyer Mousquet and SMS Karlsruhe, which sank or captured 76,909 tons of merchant shipping. Both were destroyed in early November 1914, Karlsruhe by an accidental internal explosion on the 4th and Emden by HMAS Sydney five days later.
By late November the light cruiser SMS Königsberg was the only one of the eight cruisers still afloat. She had sunk the old light cruiser HMS Pegasus at Zanzibar on 20 September 1914, and had previously sunk the 6,600 ton merchantman City of Winchester. The British then lost trace of her until the light cruiser HMS Chatham captured the German liner Präsident on 25 October. Papers found on board her indicated that Königsberg was in the Rufiji Delta in German East Africa, now Tanzania. 
Chatham spotted her masts on 30 October, but locals reported that the creek in that she was in could be mined and was defended by shore batteries and trenches. The waters were shallow, had no navigation marks and a major warship could pass them for only a few hours a day. Consequently, Königsberg was fairly safe from attack but was also trapped, since she could not hope to evade her blockaders.
On 2 November the light cruisers HMS Dartmouth and Weymouth arrived. They tried to fire on Königsberg, her supply ship Somali and the shore positions, but observation was difficult, especially as the German cruiser had removed her top masts and camouflaged herself with foliage. An attack on the Somali by a steam launch carrying two torpedoes on 7 November failed, but Chatham was able to set the Somali on fire, destroying many of the Königsberg’s stores. Three days later the British blocked what was believed to be the only navigable channel out of the Rufiji by scuttling the collier Newbridge in it. The British lost two men killed and nine wounded in this operation.
A seaplane was sent to the Rufiji, locating Königsberg on 22 November; she was out of range of any ships outside the delta. It was damaged, but returned after being repaired with a new hull that allowed it to carry an observer and bombs. A reconnaissance flight on 4 December revealed that there were two other channels that Königsberg might use, as well as the one that had been blocked. Six days later the seaplane was lost after a forced landing. 
Dar-es-Salaam was attacked on 28 November in order to destroy merchant vessels that might have supplied Königsberg. Commander Henry Ritchie was awarded the RN’s first Victoria Cross of the war for courage during it.
On 6 February the armed tug Adjutant was lost whilst investigating the entrance to the delta. The British Official History says that she was captured by the Germans and later used on Lake Tanganyika, but the Naval Staff Monograph, an internal Admiralty document, states that it was a different ship of the same name that was captured.
Two Sopwith seaplanes with 100 hp engines and capable of carrying 100 pound bombs were sent out from the UK, but they were not powerful enough for the climactic conditions, one of them crashing on 24 February. Combined operations using marines were considered but rejected.
The Admiralty commenced a formal blockade of the Rufiji on 1 March, meaning that neutral ships should leave, although none were present. The need for refits and redeployments of modern ships meant that the squadron off the Rufiji consisted of HMS Weymouth, the older light cruisers HMS Hyacinth and Pyramus and HMAS Pioneer, the armed merchant cruiser HMS Kinfauns Castle, the armed steamer Dupleix, the armed tug Helmuth and the armed whalers Fly, Pickle, Echo and Childers.
On 6 March Vice Admiral Herbert King-Hall. C.-in-C. of the Cape Station arrived at the Rufiji in the pre-dreadnought battleship HMS Goliath to take command. On 24 March Pyramus was sent for a refit. The next day Goliath was ordered to the Dardanelles, where she was later sunk. King-Hall transferred his flag to Hyacinth.
Three more Short seaplanes with 160 hp engines arrived on the armed merchant cruiser HMS Laconia on 20 April. They carried out reconnaissance flights on 25 and 27 April, taking photos of Königsberg and fixing her position. She was, however, too well camouflaged to see whether or not she had landed any of her guns. The seaplanes came under heavy fire at their maximum height in this climate of 800-1,000 feet, so King-Hall decided not to carry out further flights for now. He suggested attacking Königsberg with a torpedo armed launch, but the Admiralty had come up with an alternative plan.
On 28 April the monitors HMS Mersey and Severn left Malta for East Africa, accompanied by the fleet messenger Trent, four tugs and a collier. The monitors were shallow draft vessels designed for river operations and armed with two 6 inch guns. They struggled to make the journey, since they were not designed for the open seas or for the heat of the Red Sea, but they arrived on 3 June after a ‘voyage…as arduous as any in the war.’
King-Hall’s squadron attacked Königsberg on 6 July. Pyramus had by then rejoined and Kinfauns Castle had been replaced by the armed merchant cruiser HMS Laurentic. The cruiser HMS Challenger arrived two days later. An onshore aerodrome had now been set up.
The monitors headed up river at 4:15 am, stopping 10,800 yards from Königsberg at 6:20 am They easily dealt with machine gun and rifle fire and an attempt to launch a torpedo from the shore. They opened fire at 6:48 am, firing alternate salvos with an aeroplane spotting for them, but problems were encountered in receiving the corrections. Königsberg opened fire at 7:00 am, quickly straddling the monitors. Mersey’s captain decided to change her position after she was slightly damaged at 7:30 am, but one of her 6 inch guns was then knocked out. Six of her crew were killed and two wounded. She withdrew a short distance at 7:40 am. In the meantime, the light cruisers were bombarding suspected German positions at the entrances to the delta.
The seaplane found it easier to spot for only one monitor, and Severn began to hit Königsberg from 7:51 am onwards. Mersey returned at 8:10 am, but both monitors then started to miss the target. Severn changed position at 9:15 am, reopening fire at 9:50 am, but the aeroplane had now left because of technical problems. Around this time, Königsberg’s fire became ineffective after an onshore German observation post was found and destroyed. Another aeroplane arrived in the afternoon, but little further damage was done before the British withdrew at 3:30 pm.
The attack was resumed on 11 July, as soon as the monitors and aircraft had been repaired. This time, Mersey would move to the same position as before and open fire with the sole intention of covering Severn’s move to a different position 10,000 yards from Königsberg. The aeroplane would spot only for Severn. If she had not put Königsberg out of action in an hour, Mersey would move to 7,000 yards from the German ship and take over. If this did not work, Severn would advance to 6,000 yards range. Only one monitor would be firing at any one time to ease spotting for the aeroplane.
The monitors were in the entrance by 11:45 am. Mersey’s attempt to distract Königsberg failed, and Severn came under heavy fire. She opened fire from 9,500 yards at 12:31 pm, closing to 8,800 yards after the first five salvos had missed. At 12:42 pm, the eighth salvo hit and hits continued to be scored until 12:49 pm, when shrapnel damage forced the aeroplane to ditch near Severn. Its last signal informed the monitor that all her hits had been in the forward part of the German cruiser. Severn corrected her fire and at 12:52 pm scored a hit that produced a large explosion and dense smoke. The Germans then stopped firing.
Severn continued firing until 1:46 pm, when Mersey was ordered to close to 7,000 yards. As she advanced, Königsberg suffered a number of explosions, presumably an attempt to scuttle her since she was not then under fire. Mersey opened fire at 2:15 pm, with another seaplane spotting. She could not get closer than 8,000 yards and could bring only one gun to bear, but after 15 minutes Königsberg was on fire, listing heavily and had lost a funnel, so the British ceased fire and withdrew. Their only casualties were two men slightly wounded on Mersey.
Königsberg inflicted little damage on Allied shipping, but she was able to tie up a large number of British warships, both in blockading her and in escorting troop convoys before she was found. The survivors of her crew joined the German force under Paul von Lettow-Vorbeck that was successfully conducting guerrilla warfare in East Africa.
The Germans also armed five merchant liners as commerce raiders in 1914. Two were quickly sunk: SMS Kaiser Wilhelm der Grosse (10,400 tons sunk) by the protected cruiser HMS Highflyer on 26 August 1914 and SMS Cap Trafalgar (no ships sunk) was sunk by the armed merchant cruiser HMS Carmania on 14 September 1914. SMS Cormoran (no ships sunk), short of coal, interned herself at Guam on 14 December 1914. The other two, SMS Prince Eitel Friedrich (33,423 tons sunk) and Kronprinz Wilhelm (60,522 tons sunk), conducted successful cruises before interning themselves in Newport News on 10 March and 11 April 1914 respectively. Both ships urgently needed repairs, Prince Eitel Friedrich was almost out of coal and some of Kronprinz Wilhelm ‘s crew were suffering from beri-beri.
The sinking of Königsberg meant that there were no German commerce raiders at large. The eight warships and five converted merchant liners had sunk a total of 300,318 tons of Allied merchant shipping and five warships. Even adding in ships sunk by submarines and mines and ones interned in enemy ports, the UK lost less than 2.3 per cent of its total merchant shipping and less than 2.6 per cent of steamers of over 1,000 tons from the outbreak of war to 31 January 1915. The Allies sank, captured or interned nearly 15 per cent of the Central Powers’ steam tonnage over the same period.
The main effect of the commerce raiders was that a large number of Allied warships were used to search for them and to escort troop convoys. The main problem for the raiders was coal supply. Their threat would have been greatly reduced if Allied cruisers had been used to convoy trade, especially colliers, instead of hunting for the raiders. A second round of German surface commerce raiding began in early 1916. It used smaller and innocuous looking merchant ships that needed less coal.
 Shipping losses are from Naval Staff Monograph (Historical) vol. xxv, ‘Review of German Cruiser Warfare 1914-1918’. p. 1.
 J. S. Corbett, H. Newbolt, Naval Operations, 5 vols. (London: HMSO, 1938). vol. i, p. 338.
 Naval Staff Monograph (Historical) 1921 vol. ii, ‘East Africa to July 1916, Cameroons 1914’. ‘Monograph 10 East Africa to July 1916’, pp. 54-55.
 Ibid., pp. 56-60.
 Ibid., pp. 61-68.
 Ibid. p. 75, footnote 1; Corbett, Newbolt, Naval. vol. ii, p. 288, footnote 2.
 Naval Staff vol. ii. pp. 74-75. footnote 2, p. 75.
 Ibid., pp. 77-78.
 Ibid., pp. 79-82.
 Ibid., pp. 92-93.
 Corbett, Newbolt, Naval. vol. iii, p. 64.
 Ibid. p. 64, footnote 2.
 Naval Staff vol. ii. pp. 96-97.
 Ibid., pp. 97-99.
 Ibid., pp. 99-100.
 Ibid., pp. 100-101.
 Ibid., p. 101.
 Naval Staff vol. Xxv. pp. 12-13.
 C. E. Fayle, Seaborne Trade., 3 vols. (London: HMSO, 1920). vol. i, pp. 384-86.
 Naval Staff vol. Xxv. p. 3.