Lucien B. McDonald, Lamprey cleared Fremantle 21 May and entered the Java Sea bound for her patrol area in the Siam Gulf.

The submarine returned to sea 26 July for her third war patrol and spent most of her time searching for targets along the Gulf of Siam.

She entered the Singapore area 8 August to patrol west of Pengiboe Island where she sank a small craft with gunfire.

On 21 July 1960 she was transferred on loan to the Government of Argentina and was commissioned in the Argentine Navy as ARA Santiago del Estero (S-12).

[6] Some years ago, Argentinian officials disclosed that a group of tactical divers had carried out an incursion on the Falkland Islands on board the Santiago del Estero in October 1966.