HMS Untiring (P59) was a Royal Navy U-class submarine built by Vickers-Armstrong.

So far she has been the only ship of the Royal Navy to bear the name Untiring.

After the war, she was loaned to the Greek Navy and renamed Xifias (Y-10).

After a work up patrol off the Norwegian coast, where she sank the Norwegian fishing vessel Havbris I[1] whilst she was fishing for halibut, Untiring was assigned to operate in the Mediterranean.

Untiring survived the war and was loaned to the Greek Navy in July 1945, where she was renamed Xifias.