Len Williams’s extraordinary naval career included two wartime sinkings, three years as a Far East prisoner of war and, in 1949, participation in the famous “Yangtze dash” of the frigate Amethyst. As chief engine room artificer, he was the first to start up the engines of the newly built Royal Yacht Britannia, finally serving in her for 12 years.

Leaving school at 15, Williams was apprenticed to an Ipswich engineering company until joining the Navy as an engine room artificer apprentice at HMS Caledonia at Rosyth in 1937. He was rapidly promoted to chief petty officer, his first ship being the destroyer Stronghold based at Singapore. This was followed by a posting to the river gunboat Dragonfly.

Dragonfly and her sister ship Grasshopper were used in support of British and Gurkha soldiers during the disastrous retreat down the Malay Peninsula, which ended in the fall of Singapore on February 15, 1942. These two ships were among the last to leave Singapore, loaded with VIPs and a few civilians, Grasshopper taking mainly women and children.

They were attacked south of Singapore by fighter-bombers. Dragonfly steered out to sea to try to draw attacks away from Grasshopper, but both were hit. Grasshopper managed to beach herself on Sinkep island while Dragonfly sank quickly after two direct hits. A few survivors managed to reach Sinkep island after several hours in the water. These included a dog, Judy, which became a mascot and, having located some fresh water, “a lifesaver for the women and children that had survived”.

By boat, road and rail, many reached the port of Padang on the other side of Sumatra, but air attacks prevented rescue from Ceylon (now Sri Lanka)and all were taken prisoner on March 17. Williams records that “thus began 3-4 years of the most horrific labour, torture, starvation and every degradation the Japanese could inflict on us”. Prisoners were taken to Medan in the north of Sumatra and worked in the docks and building a shrine to Japanese dead. Judy had puppies, one of which was given to the camp commandant for his girlfriend and another smuggled into the women’s camp with any food that could be spared. Years later Williams heard from a woman, who as a child had lost her mother in the camp — she had never forgotten the puppy and the food.

In June 1944 about 800 prisoners were battened down in the 3,000-ton Harukiki Maru — formerly the Dutch coaster Van Waerwijk. In convoy for Japan this vessel was sunk in the Strait of Malacca by the British submarine Truculent, the official history noting that this ship “unfortunately was carrying prisoners of war”. Williams recalled that Judy, who had been smuggled on board in a sack, was pushed through a porthole, he managing to free a hatch which fell back and damaged his leg. Though 173 prisoners died, more than 500 miraculously survived the torpedoing as well as being shot at in the water and Japanese indifference. Judy was famed for helping those wounded in the water by pushing debris towards them.

Arriving at Singapore, they were met by their camp commandant and returned to Sumatra where they were put to work on the Pekan Baru railway, which went for 300 miles through the jungle to Port Aceh. “Every sleeper laid cost lives,” said Williams, who told how they were still working at the end of the war when discovered by Lady Mountbatten and her staff. “Surviving prisoners were in a terrible state of health, emaciated and needing medical help for tropical diseases.”

Williams returned home in November 1945 after six years in the Far East. For her various services, Judy was awarded the Dickin Medal, the animals’ VC.

Returning to the Far East again in 1948, Williams was appointed to the frigate Amethyst. In April 1949, with civil war raging in China, she was ordered up the Yangtze to support the British Embassy at Nanking. Ostensibly neutral between Chinese Nationalists under Chiang Kai-Shek and the Communists under Mao Zedong, Amethyst nevertheless came under fire from Communist shore artillery and was badly damaged, suffering 53 hits which killed 15 of her crew, including her commanding officer and the surgeon and his mate. Having extricated herself from a mudbank, Amethyst anchored upstream clear of the communist batteries and evacuated many of her crew, leaving 40 not wounded, 12 wounded and the dead on board.

Attempted rescue operations by the destroyer Consort and the cruiser London failed with many casualties. A replacement captain, the assistant naval attaché from Nanking, Lieutenant-Commander John Kerans, got on board with the help of a Nationalist landing craft. Negotiations dragged on for three months, the Communists trying to make Britain admit responsibility for the incident and compensate for the Chinese who had been killed. As the Chinese attitudes hardened, Kerans decided to attempt a breakout. On the night of July 31, Amethyst slipped her anchor cable and set off, luckily being able to follow close behind a passenger steamer and confusing the gunners on shore. She then navigated 104 miles of river at full speed, emerging past the forts at Woosung with the celebrated signal: “Have rejoined the Fleet. God save the King.”

The ship’s cat, Simon, was also awarded the Dickin Medal; service with two such winners conferring another unique dimension to Williams’s naval service.

The daring operation produced an enormous wave of public acclaim, Kerans being awarded the DSO. For his vital work in keeping Amethyst’s engines running, Williams was awarded the DSM.

He then served in the cruisers Cumberland and Devonshire in the Mediterranean and West Indies. He was chosen in July 1953 to join the Royal Yacht Britannia, under construction in John Brown’s yard at Glasgow: “Then followed 12 wonderful years, with three round-the-world trips and visiting so many countries with wonderful welcomes.” He left Britannia and the Navy in 1964, attending Britannia’s decommissioning ceremony in 1997.

He went to teach at Portsmouth Polytechnic (now the University of Portsmouth) in the engineering and naval architecture department and worked there for 20 years.

He is survived by his wife, Dorothy Woodley, whom he married in 1951, and his stepson by her first marriage, to a Seaforth Highlander who was killed on the last day of the war.

Chief Petty Officer Leonard Williams, DSM, naval engineer, was born on July 24, 1919. He died on December 14, 2006, aged 87