5 Sep, 1939
HMS Neptune (Capt. J.A.V. Morse, DSO, RN) intercepts the German merchant Inn (2867 GRT) off the Canary Islands. However before the ship can be capture she is scuttled by her own crew.

Nov, 1939
Remained in the South Atlantic as part of Force "K", looking for the Admiral Graf Spee.
In May 1940 transferred to the Mediterranean and joined the 7th Cruiser Squadron.

22 Nov, 1939
The German passenger ship Adolph Woermann (8577 GRT) is intercepted in the South Atlantic about 530 nautical miles east-south-east of Ascension in position 10º39S, 05º44W by the British light cruiser HMS Neptune (Capt. J.A.V. Morse, DSO, RN). However before the German ship can be captured she is scuttled by her own crew. (see map)

11 Jun, 1940
Neptune sortied from Alexandria with the Mediterranean Fleet and elements of the French Fleet for a naval demonstration south of Crete. The Fleet bombarded Italian positions on the Libyan coast, Neptune shelling Bardia before retuning ot base on 14/6.

Jul, 1940
Neptune was present at the Battle of Punta Stilo on 9 July then moved back to the Eastern Med, scouting into the Gulf of Athens with HMAS Sydney and sinking a small tanker.
The appearance of more German raiders in the Atlantic caused her redeployment to Freetown, Sierra Leone, by November 1940.

May, 1941
Under refit at Chatham from February to May. On completion of the work hunted for the German supply ships intended to support the Bismarck.
On 4 June 1941 assisted in the interception of Gonzenheim, sinking her by torpedo north of the Azores in position 43º29'N, 24º04'W. (see map)

29 Nov, 1941
Transferred to Force "B", based on Malta. On arrival she was allocated to Force "K".

1 Dec, 1941
Acting on an ULTRA intercept, a British force sailed from Malta in the evening of 30 November with the British light cruisers HMS Neptune (Capt. R.C. O'Conor, RN), HMS Aurora (Capt. W.G. Agnew, RN), HMS Ajax (Capt. E.D. McCarthy, DSO and Bar, RN), HMS Penelope (Capt. A.D. Nicholl, RN) and the British destroyers HMS Kimberley (Cdr. J.S.M. Richardson, DSO, RN), HMS Kingston (Cdr. P. Somerville, DSO, DSC, RN) and HMS Lively (Lt.Cdr. W.F.E. Hussey, DSC, RN).
At 0330 hrs of 1/12 the British intercept and sink the Italian transport Adriatico (1976 GRT) then proceed towards the Lybian coast.
At a point 60 nautical miles north-north-west of Tripoli, Libya, Penelope, Aurora and Lively intercept a small convoy consisting of the Italian oiler Iridio Mantovani (10540 GRT) escorted by the Italian destroyer Alvise da Mosto (2125 tons) and sink both.

19 Dec, 1941
While on their way to intercept an Italian convoy bound for Tripoli the British Force K (light cruisers HMS Neptune (Capt. R.C. O'Conor, RN), HMS Aurora (Capt. W.G. Agnew, RN), HMS Penelope (Capt. A.D. Nicholl, RN) and the destroyers HMS Kandahar (Cdr. W.G.A. Robson, DSO, DSC, RN, HMS Lance (Lt.Cdr. R.W.F. Northcott, RN), HMS Lively (Lt.Cdr. W.F.E. Hussey, DSC, RN) and HMS Havock (Lt. G.R.G. Watkins, DSC, RN) ran into an newly laid Italian minefield. HMS Neptune and HMS Kandahar sank while HMS Aurora was badly and HMS Penelope was lightly damaged. HMS Aurora was patched up at Malta before returning home for repairs at Liverpool from April to June 1942. HMS Penelope was repaired at Malta but was bombed on 26 March 1942 while still under repair. She left Malta on 8 April 1942 for full repairs at the New York Navy Yard in the USA. These repairs were completed in September 1942.