The Amethyst Incident, also known as the Yangtze Incident, in 1949 involved the Black Swan class sloop HMS Amethyst being trapped on the Yangtze River for three months, during the Chinese Civil War. On 20 April 1949, HMS Amethyst, commanded by Lieutenant Commander Bernard Skinner, was on her way from Shanghai to Nanking to relieve HMS Consort, which was standing as guard ship for the British Embassy there . According to the Royal Navy, at around 0831, after a burst of small arms fire, a People's Liberation Army (PLA) gun battery fired a salvo of ten shells, which fell well short of the ship, and was assumed to be part of a regular bombardment of Nationalist forces on the south bank. 

Speed was increased, and large Union Flags were unfurled on either side of the ship, after which there was no more firing.  At 0930, as the frigate approached Kiangyin further up the river, she came under sustained fire from a second PLA battery. The first shell passed over the ship, then the bridge, wheelhouse and low power room were hit in quick succession, the captain was mortally wounded, and all the bridge personnel were disabled. The coxswain on the wheel was seriously injured and as a result the ship slewed to port and grounded on the bank before control of the ship was resumed. Before the ship was hit, the order to open fire had been given, but when the director layer pulled the firing trigger, nothing happened, because the gun firing circuits were disabled when the low power room was hit. The first lieutenant, Geoffrey L. Weston, assumed command of the vessel, though wounded.  PLA shells exploded in the sick bay, the port engine room, and finally the generator, just after the injured Weston's last transmission: "Under heavy fire" am aground in approx. position 31.10' North 119.50' East. Large number of casualties".

By the time the shelling stopped at about 1100, 22 men had been killed and 31 wounded in all. Amethyst had received over 50 hits and holes below the waterline were plugged with hammocks and bedding. During this time the destroyer HMS Consort was sighted, flying seven White Ensigns and three Union flags, steaming down from Nanking at 29 knots following an order to do so from Admiral Madden, the Flag Officer, second in command, Far East Station. The frigate HMS Black Swan was also steaming towards Amethyst from Shanghai. Consort reached the Amethyst at about three in the afternoon and was immediately heavily engaged. She found the fire too heavy to approach Amethyst and therefore passed her at speed down river. She turned two miles below and again closed Amethyst to take her in tow. But again she came under such heavy fire that she was obliged to abandon the attempt, although she answered the shore batteries with her full armament and signaled that she had silenced most of the opposition. Half an hour later she again made an attempt to take Amethyst in tow. This attempt also failed and she sustained further damage and casualties during which her steering was affected. She had to continue downstream out of the firing area with 10 men killed and 23 injured

The Assistant British Naval Attaché, Lieutenant Commander John Kerans, joined the ship on 22 April and took command. On 30 July 1949 Amethyst slipped her chain and headed downriver in the dark, beginning a 104 mile dash for freedom running the gauntlet of Communist guns on both banks of the river. She followed the passenger ship Kiang Ling Liberation in the hope that the observers ashore would be confused and not see Amethyst in the dark. When the battery opened fire, the fire was directed at the Kiang Lin Liberation which was sunk by the gun fire, with heavy civilian casualties. 

At 0500 hours on 31 July, Amethyst approached the PLA forts at Par Shan and Woosung with their searchlights sweeping the river. At 0525 a pre-planned meeting with the destroyer HMS Concord took place. Concord had been ordered to prepare to provide gun support to Amethyst if she came under fire from the shore batteries at Woosung. To achieve this she had moved up the Yangtze during the night, at action stations. Fortunately, Amethyst was not spotted by the shore batteries and the two ships then proceeded down river until at 0715 they stood down from action stations and cleared the river mouth and anchored. After a short stay at anchor, Concord lent Amethyst sailors to fill gaps in her ship's company and the two ships set sail for Hong Kong. 

Amethyst transmitted the following signal to Admiralty "Have rejoined the fleet south of Woosung ... No damage... No casualties....God save the King!"