Following her re-fit at Portsmouth Ajax was recommissioned on 11th January 1938 and sailed on her 2nd Commission under Captain Charles Henry Lawrence Woodhouse to join the America & West Indies Squadron. He was captain from 9th October 1937 to 22nd April 1940.
When in Chilean waters with Exeter they rendered humanitarian aid at the terrible earthquake in the Chillán and Concepción region on 24th January 1939 that devastated the region and killed over 30,000 residents. Both ships left the region on 3rd February 1939.
3 hours after the outbreak of war on 3rd September 1939 Ajax intercepted the German freighters OLINDA & CARL FRITZEN between Rio Grande do Sul & Plate estuary. Both ships scuttled to avoid capture.
On 27th October 1939 Commodore Harwood transferred his Broad Pennant to Ajax and commanded the Hunting Group G; Ajax, Achilles, Exeter & Cumberland.
Following The Battle of the River Plate Ajax (see additional pages) made for the Falklands when it was decided she would be repaired back in the UK. En route on 3rd January 1940 she called at Montevideo on a goodwill visit while Achilles went to Buenos Aires.
The Commodore transferred his flag to Achilles and Ajax left for Freetown on the way back to the UK. Ajax would never sail with Exeter or Achilles again.
On 31st January 1940 Ajax arrived at Plymouth for repairs and the Ship's company was reviewed by King George VI and a luncheon held at the Guildhall London.
The next day, the 24th February 1940 Ajax left Devonport, Plymouth for Sheerness joining Nore Command Shore-based Division out of Chatham for a full refit at Chatham.
This would take until 28th July 1940 when she would be assigned to the Mediterranean. Whilst under refit her retained crew were assigned to duties at the Dunkirk evacuations in the May & June 1940.