The Australian Prime Minister, Harold Holt, disappeared after going for a swim in the ocean on December 17th 1967 - never to be seen again. Susan Hulme has been speaking to Martin Simpson who was with the group that went to the beach with the Prime Minister that day.

Photo: Harold Holt on the beach with three women the year before his disappearance. Credit: Evening Standard/Getty Images

In December 1967, the great American soul singer, Otis Redding, was killed in a plane crash as he stood on the brink of superstardom. Simon Watts introduces the memories of Otis’s guitarist, Steve Cropper, and trumpeter, Wayne Jackson, as recorded in the BBC archives.

(Photo: Otis Redding in 1967)

Thousands died as a thick polluted fog engulfed London in 1952. People with respiratory and cardiovascular conditions were most at risk. The smog was a combination of pollution from millions of coal home fires and freezing fog. Unusual atmospheric conditions trapped the pall over the city for four days. The civil disaster changed Britain. Two years later, the government passed the Clean Air Act to reduce the use of smoky fuels such as coal. Alex Last speaks to Dr Brian Commins, who worked for the Medical Research Council's Air Pollution Unit set up at St. Bartholomew's hospital in London in the 1950s.

The African-American lab technician, Vivien Thomas, whose surgery helped save the lives of millions of babies but whose work went unrecognised for years. Claire Bowes has been listening to archive recordings of Vivien Thomas describing his long partnership with Dr Alfred Blalock, the man solely credited with inventing an operation in 1944 which helped manage a congenital heart defect called Tetralogy of Fallot.

(Photo: Vivien Thomas, US Surgical Technician, 1940)

In 2001, American hypnotist Larry Garrett was invited to Iraq to treat an "important businessman". When he arrived in Baghdad he was told his special patient's true identity: Uday Hussein, the volatile and violent eldest son of Iraqi leader Saddam Hussein. Mike Lanchin speaks to Garrett about the time he spent with Uday, about their long conversations and how he coped with the challenges of treating one of the most feared men in Iraq.

Photo: Larry Garrett in Baghdad, 2001 (courtesy of Larry Garrett)

The Russian Revolution of 1917 led not just to huge political and social change, but to a new artistic freedom. Russian avant-garde artists like Malevich, Kandinsky and Chagall flourished in the immediate aftermath of the revolution. One of their greatest supporters was art curator Nikolai Punin. Louise Hidalgo has been talking to Punin's granddaughter, Anna Kaminskaia, about how that freedom was gradually replaced with censorship and repression, and her grandfather ended his life in the Gulag.

Picture: 1920 painting by Boris Mikhailovich Kustodiev (1878-1927), Bolshevik (oil on canvas), Tretyakov Gallery, Moscow, Russia

In 1967 a biologist began listening to strange sounds recorded way out at sea, he realised it was whales and that they were singing. Claire Bowes has been talking to Dr Roger Payne about the discovery that helped change people's perception of whales and helped found the modern conservation movement at a time when whales were close to extinction.

(Photo: Humpback Whale, courtesy of Christian Miller of Ocean Alliance)

In December 1917 Finland proclaimed its independence. For many centuries it had been controlled by its powerful neighbours, Sweden and Russia. As World War One raged across Europe and Russia was embroiled in its own revolution, Finnish intellectuals took the opportunity to push for their own state. But many ordinary people were more concerned with dire food shortages and the chaos caused by conflict. Olga Smirnova hears memories of that time.

(Photo: 1917: A Communist base burning during the Finnish civil war. Credit: Getty Images)

More personal stories from history of independent Finland can be found at the Finnish Institute in London http://www.taleoftwocountries.fi/frontpage/

In 1967 the British withdrawal from their colony of Aden led to the creation of the People's Republic of South Yemen. Britain had colonised the port city in 1839. Aden had been at the centre of the British colonial trading system and had been one of the busiest ports in the world. The handover has been described as one of the most chaotic in British colonial history. Farhana Haider has been speaking to the former British diplomat, Oliver Miles and to Ghassan Luqman who says the scars of Britain's quick withdrawal are still being felt in Yemen today.

Photo: Aden 1967 Copyright: Alamy.

The four huge granite heads of former presidents on Mount Rushmore have become one of America's most famous monuments. Construction started on the site in 1927, led by sculptor Gutzon Borglum. His granddaughter Robin Borglum Kennedy speaks to Lucy Burns about his work.

Picture: Mount Rushmore, June 1995 (KAREN BLEIER/AFP/Getty Images)