On 6 October 1917, Nahma was involved in a series of friendly fire incidents. At 19:00 on 5 October, she was on patrol in the Atlantic Ocean west of Gibraltar when she received a radio report of an Imperial German Navysubmarine in the vicinity and proceeded toward its reported position. At 02:00 on 6 October she sighted a flash ahead which resembled the flash of a gun. At 02:30 she sighted the Italian cargo shipSS Bologna, followed by two submarines. Bologna was on a voyage from Bermuda to Gibraltar as part of a convoy that was running five days behind schedule, and the submarines were the Regia Marina (Italian Royal Navy) submarines H6 and H8, two of the three submarines serving as escorts for the convoy. The third escorting submarine had become separated from the convoy in fog after the reported sighting of a German submarine.[4]
Having earlier received a report of enemy submarine activity in the area and seen what appeared to be a flash of gunfire, Nahma′s crew assumed that H6 and H8 were German submarines attacking Bologna. She opened gunfire, firing two rounds at the leading submarine, H8, neither of which hit, and made a recognition signal challenge. When H8 did not respond, she fired two more rounds, then ceased fire when H8 responded correctly to the challenge. Nahma then approached H6 and observed members of H6′s crew running aft along her deck. They were going to hoist the Italian colors, but Nahma assumed they were going to man H6′s deck gun and fired one round. It hit H6′s conning tower, killing two men and wounding seven others, two of whom later died of their wounds. Nahma then identified H6 as friendly, ceased fire, and stood by to assist H6 for the remainder of the night.[4]
At about 05:00 on 6 October 1917, the British torpedo boatHMS TB 93 arrived on the scene and accidentally fired one round toward Nahma. It missed, and Nahma headed toward the flash. At 05:20 she sighted TB 93 and mistook her for a German submarine. She opened gunfire, firing two rounds at TB 93 before identifying her as friendly. On the morning of 6 October, Nahma escorted H6 and H8 to Gibraltar.[4]
Nahma continued her escort duties through the armistice with Germany, which brought World War I to an end on 11 November 1918. Following the war, she remained in the Mediterranean for relief and quasi-diplomatic work. Operating in the Aegean Sea and Black Sea, she carried relief supplies to refugee areas; evacuated American nationals, non-combatants, the sick, and the wounded from areas of Russia and Turkey affected by the Russian Civil War and the Turkish War of Independence; and provided communications services between ports. She was decommissioned at Greenock, Scotland, on 19 July 1919 and returned to Robert Walton Goelet.[2]
By March 1931, Istar had been laid up at Port Natal, South Africa, and she was sold for scrap that month.[2] Rather being scrapped, however, she was scuttled in the Indian Ocean 7 kilometres (3.8 nmi; 4.3 mi) outside the harbour at Durban, South Africa, on 28 March 1931.[7][2]
