During the First World War, the British laid large numbers of mines in the Helgoland Bight in an attempt to prevent U-boats travelling to the Atlantic via the North Sea. The Germans sent minesweepers up to 100 miles from Heligoland almost every day in an attempt to clear them. They were normally escorted by light cruisers and torpedo boats, with battleships sometimes covering them. By mid November 1917 the British Admiralty had enough intelligence on German operations to plan an attack on the minesweepers and their escorts.
The British striking force that sailed from Rosyth on the Firth of Forth at 4:30 pm on 16 November comprised: 1st Cruiser Squadron (Vice Admiral Trevelyan Napier) of two light battle cruisers and four destroyers; 6th Light Cruiser Squadron (Rear Admiral Edwyn Alexander-Sinclair) of four C class light cruisers and four destroyers; 1st Light Cruiser Squadron (Commodore Walter Cowan) of one C and 3 Arethusa class light cruisers and two destroyers; and 1st Battle Cruiser Squadron (Vice Admiral William Pakenham (five battlecruisers, a light cruiser and eight destroyers.
Pakenham was in overall command of the operation, but Napier commanded the two light cruiser squadrons as well as his own cruiser squadron.
The 1st Battle Squadron of six battleships and 11 Destroyers was in a supporting position several hours steaming away.
The Germans had the VI Minesweeping Group, II and VI Support Groups and IV Barrier Breaker Group, totalling 16 auxiliaries and a similar number of trawlers, escorted by eight destroyers of the 7th Torpedo Boat Flotilla and the four light cruisers of the II Scouting Group (Konteradmiral Ludwig von Reuter). Two German battleships were in support near Heligoland.
The light battlecruisers, HMS Courageous and Glorious, were fast (32 knot), lightly armoured ships armed with four 15 inch, 18 4 inch and two 3 inch guns plus two 21 inch torpedo tubes. They had very shallow drafts and had been intended to take part in operations in the Baltic, which were cancelled when Admiral Lord Fisher ceased to be First Sea Lord. Fisher called them large light cruisers in order to evade a government order forbidding the construction of more capital ships.
The British spotted German ships at 7:30 am on 17 November, opening fire seven minutes later. The Germans destroyers and light cruisers turned towards the British and covered the minesweepers with a smokescreen. All withdrew except the armed trawler Kehdingen, which had been hit and immobilised. The other German ships were in the smoke before the British could ascertain their strength.
The German ships became visible briefly and were fired on but the situation remained unclear until 8:07, when Napier’s flagship Courageous cleared the smoke, allowing him to see three German light cruisers to the south east, steering east north east. Four minutes later they changed course to the south east.
The German auxiliaries were now to the north east and were not being pursued. Reuter could therefore draw the British through the minefields towards the German battleships. The British could fire only their forward guns at his light cruisers but a single hit by a 15 inch shell on one of them could slow her by a few knots, meaning that he would have to abandon her, as Admiral Franz von Hipper had had to do with SMS Blücher at the First Battle of Heligoland Bight in 1915.
Courageous and Glorious opened fire at 8:10, but it was another 10 minutes until all the British ships were in range of the Germans. They then laid another smokescreen and 15 minutes later disappeared into dense smoke. Napier was now at the edge of the British minefields and turned to port, considering that the situation was too uncertain to risk continuing. The light cruisers followed just after 8:40. The 6th Light Cruiser Squadron made the smallest turn and HMS Cardiff was hit and damaged at 8:50. The smokescreen was now clearing, revealing that the Germans had not changed course. 
Napier’s squadron had lost five miles and was now at extreme range, although the 6th Light Cruiser Squadron and HMS Caledon of the 1st Light Cruiser Squadron were closer.
The British opened fire again at 8:52. Napier decided to follow the Germans for 12 more miles, which would take his force to the edge of an area that the Admiralty had in 1915 labelled as being dangerous because of mines. His force had now been reinforced by the battlecruiser HMS Repulse, which had been ordered by Pakenham not to enter the minefields.
At 8:58 Pakenham ordered the British to withdraw. He had received a signal from Napier at 8:52 that implied that contact with the Germans had been lost permanently but actually meant that they had temporarily disappeared behind a smokescreen. All British ships were in action by the time that Pakenham’s withdrawal order was received, and it was disregarded.
Firing was intermittent, but the British believed that they had damaged at least one German cruiser. The Germans launched an unsuccessful torpedo attack around 9:30. At 9:32 Napier took Courageous and Glorious out of the action because they had reached his danger line, but the light cruisers, whose commanders did not have the chart Napier had based his decision on, continued. At 9:40 HMS Calypso was damaged, but the British appeared to have the advantage until 9:50, when shells from two German battleships started to land amongst them. The light cruisers withdrew, covered by Repulse. The Germans did not pursue them and a thick fog descended at 10:40.
The British thought that some of the eight or 10 torpedoes fired at them came from a U-boat but none were present.
The Germans repeatedly straddled the British ships but scored only seven hits, all on the light cruisers. The British managed only five hits, with SMS Königsberg being the only German ship seriously damaged. A shell from Repulse penetrated her three funnels and exploded over one of the boiler rooms. Her repairs were completed on 15 December.
Naval-History.net lists 22 British sailors killed at the Second Bight of Heligoland Bight, all of them on light cruisers. None of the sources consulted give German casualties. One of the British dead, Ordinary Seaman John Carless of HMS Caledon, was awarded a posthumous Victoria Cross. Carless, who had joined the Royal Navy in September 1915 after being rejected by the army four times because of a weak heart, remained at his post and continued to load his gun despite being severely wounded. The citation for his VC, quoted on Wikipedia, stated that:
For most conspicuous bravery and devotion to duty. Although mortally wounded in the abdomen, he still went on serving the gun at which he was acting as rammer, lifting a projectile and helping to clear away the other casualties. He collapsed once, but got up, tried again, and cheered on the new gun’s crew. He then fell and died. He not only set a very inspiring and memorable example, but he also, whilst mortally wounded, continued to do effective work against the King’s enemies.
— The London Gazette, No. 30687, 17 May 1918
The British failure to pursue more effectively was partly due to the light cruiser admirals not having all the information about minefields available to the Admiralty and to Napier. Additionally, Napier pursued at 25 knots when Courageous and Glorious were capable of at least 30 knots and were superior to the German light cruisers that they were chasing.
The only vessel sunk in the battle was the German Kehdingen but losing only one trawler when so heavily outnumbered was a success for the Germans in an action where the British might have sunk a large number of minesweepers, destroyers and cruisers.
 J. S. Corbett, H. Newbolt, Naval Operations, 5 vols (London: HMSO, 1938). vol. v, pp. 165-66.
 M. Faulkner, A. D. Lambert, The Great War at Sea: A Naval Atlas 1914-1919 (Barnsley: Seaforth, 2015), pp. 138-39; A. J. Marder, From the Dreadnought to Scapa Flow; the Royal Navy in the Fisher Era, 1904-1919, 5 vols (London: Oxford University Press, 1961-70). vol. iv, pp. 300-1,
 R. Gray, Conway’s All the World’s Fighting Ships, 1906-1921 (London: Conway Maritime Press, 1985), pp. 39-40.
 Corbett, Newbolt, Naval. vol. v, pp. 169-70.
 Ibid., pp. 170-71.
 Ibid., p. 171.
 Ibid., p. 172.
 Marder, From. vol. iv, p. 302.
 Corbett, Newbolt, Naval. vol. v, pp. 172-73.
 Ibid., p. 173.
 Ibid., pp. 175-76.
 Marder, From. vol iv, p. 305.
 Ibid., p. 304.
 Corbett, Newbolt, Naval. vol. v, p. 177; Marder, From. vol. iv, p. 305