The Net class boom defence vessels were a fleet of eleven vessels built between Blyth Shipbuilding and Drydock Co. Ltd. (6 vessels), Smith’s Dock Co Ltd,. Haverton Hill (2 vessels), Lobnitz and Co Ltd., Renfrew (2 vessels) and Cockatoo Docks and Engineering Co Ltd, Sydney, Australia (1 vessel). These vessels measured 159.7′ x 30.7′ x 13.0′ and displaced 530 tons. The Barnehurst was launched from Blyth and was immediately renamed Bayonet. She was powered by a reciprocating vertical triple expansion engine, single shaft, by North East Marine Eng‘g delivering 850 ihp. These vessels were armed with a single 3 inch deck gun. Bayonet’s Naval number was Z05.
The loss of HMS Bayonet on 21st December 1939 has been a case of confusion and deception for many years. A war memorial close to the site of her loss attributes the sinking to a collision with a German mine laid by the German submarine U-21 ( Fritz Frauenheim) on 4th November 1939. In fact, the German U-boat laid her mines on the north side of the river closer to Rosyth and could not have planted mines in the shallow water near Leith. It was perhaps convenient to the British cause at the time to blame the loss on the German minefield but the actual cause of the loss was kept secret until official records were released fifty years later.
The true nature of the loss is revealed in records of court martial of her skipper A. Lamont, RNR held following the loss. Bayonet was in a position 21.5 degrees 6.56 cables from the Martello Tower at the entrance to Leith Dock when she was destroyed by an explosion as she collided with a mine. She sank within five minutes but thankfully most of the crew managed to escape before she went down. Three crewmen lost their lives in the incident.
The minefield that caused the loss of Bayonet was actually laid only one day earlier by HMS Plover as a defensive minefield for Leith dock and Bayonet was performing her role managing the boom that guarded the entrance to the dock. Despite the findings of the first court martial that cleared Lamont of wrong doing based on Lamont’s own testimony a second court martial found him guilty of negligence and showed that Lamont had lied at the first inquiry. It appears that Lamont had seen Plover laying the mines the previous day and used only this sighting as his guide to the location of the minefield and neglected to take any specific measurements of his exact location. This turned out to be a fatal error as his ship ran into one of the mines laid by Plover and quickly sank.
The wreck lay close to the fairway entrance to the dock so it is certain that the remains were either removed of dispersed soon after the loss to clear the access to the port. Based on the location given during the court martial, an approximate position for any remains would be near to 55° 59.815’N, 03° 10.141’W.