Built by Hall Russell and Co Ltd, for the Aberdeen Steam Trawling an Fishing Co Ltd and launched on 7th December 1916 , the steel steam trawler Strathrannoch was immediately requisitioned by the Royal Navy for duties as a minesweeper and entered service in January 1917. She measured 117.7′ x 22.1′ x 12.2′ and weighed 215 gross tons, 93 net tons. She was powered by a triple expansion steam engine by Hall Russell. 74 nhp. For naval service she was fitted with a single 6pdr gun for anti aircraft use.
On 5th April Strathrannoch and another trawler minesweeper Ratapiko joined minesweeper unit No 9 assigned to sweep the area east off St Abbs Head. The unit was commanded by Lieutenant Alexander Robertson aboard the trawler Scarron. The Strathrannoch was commanded by her skipper William Bowles with a full crew of twelve men aboard. When off St Abbs Head one of the trawlers, Sophron, spotted a floating mine which was successfully exploded by rifle fire. Robertson immediately reported the sighting and destruction of the mine to the senior officer at Granton and took the unit back to base at St Abbs. As the small fleet headed to St Abbs Robertson received a signal to send two armed trawlers to Girdleness for escort duty. He assigned Strathrannoch and Ratapiko and signalled instructions to the two skippers to head north the following day.
Early the next morning Unit No 9 were ordered back to St Abbs Head to sweep the area off the headland and Strathrannoch and Ratapiko set out to their assigned duty off Girdleness. At around 10.45am another mine was swept up by Sophron and destroyed by gunfire. 15 minutes later Robertson heard a muffled explosion which he initially thought to be gunfire. He continued with the sweeping duties until, later, it transpired that the Strathrannoch was missing. It was later discovered that a signalman ashore in the Coastguard Station had seen the explosion which had sunk the Strathrannoch less than a mile offshore. He described a blast followed by a huge spout of water and debris and when the sea settled down the vessel had completely disappeared. All thirteen men aboard were lost despite the efforts of a number of local fishing boats which rushed to the scene.
The mine that had sunk the Strathrannoch had been laid by UC-31 under the command of Oberleutnant Otto von Schrader only the previous day, the UC-31 laid Barrage 55, 55a and 55b on 5 March 1917 and the Strathrannoch hit a mine in Barrage 55.
The wreck of the Strathrannoch lies in two large pieces in position 55° 54.876’N, 002° 06.745’W in 56 metres oriented 000°/180°. Presumably the strength of the explosion split the vessel in two sinking it instantly.