What was Operation Grapple? Call the Midwife highlights effects of nuclear tests at Christmas Island

Since then, Derek and his wife have struggled to conceive; and when their son is born, he does not live long. His friend Bobby's daughter was also born with missing fingers, and many of the veterans have experienced poor health.

Call the Midwife has a proud history of highlighting public health scandals and real-life conditions, and this episode is no exception. If your interest has been piqued and you want to know more, here are all the details of what really happened.

Operation Grapple: what happened on Christmas Island?

Operation Grapple was a crucial part of the British mission to develop a hydrogen bomb. The Cold War was well underway by the mid-1950s; at that time, the world's only two thermonuclear powers were the USSR and the USA – but the British authorities wanted to possess thermonuclear weapons of their own. The British had already built and tested an atomic bomb (like those used in Hiroshima and Nagasaki) but a hydrogen bomb would be a far more destructive weapon to have in the nuclear arsenal, and would also increase Britain's standing on the international stage.

Several hydrogen bombs were designed and produced, and in 1957 the British military arranged the first test. That had always been the plan; as Prime Minister Anthony Eden had said on the radio two years beforehand, "You cannot prove a bomb until it has exploded. Nobody can know whether it is effective or not until it has been tested."

The locations chosen were Malden Island (Independence Island) and Kiritimati (Christmas Island) in the South Pacific Islands, which are part of modern-day Kiribati. These beautiful, remote islands were part of the British colonies until 1979, and – despite having a population of several hundred islanders – they were was subjected to nine nuclear explosions between 1957 and 1958.

Operation Grapple was a massive operation. During this time, approximately 20,000 British servicemen were deployed to Kiritimati (Christmas Island), alongside several hundred New Zealand and Fijian soldiers. Many of the British servicemen were on their National Service, a programme of post-war conscription which required all healthy men aged 17-21 to serve in the armed forces for 18 months (later increased to two years). It was introduced in 1949, and call-ups finally ended in 1960.

The military ran four test series, trying out several different hydrogen bombs. After some disappointing results with the first few designs, Britain ultimately joining the ranks of the world's recognised thermonuclear powers by successfully testing a hydrogen bomb. This led directly to the restoration of the nuclear "Special Relationship" with the United States.

After a four-year pause, there was another onslaught of nuclear testing at Christmas Island in 1962, when the UK cooperated with the US on Operation Dominic to carry out a further 31 detonations.

What was it like to experience a nuclear test?

In the episode, Bobby Delamore (Kieran Hill) shows Dr Patrick Turner (Stephen McGann) and Shelagh Turner (Laura Main) some cine film he captured during his National Service, which he smuggled out thanks to his job in the post room.

"I was on the shore," he tells the Turners. "Mushroom hung in the air 40 minutes, nearly an hour, just like you see on those news reels of Hiroshima. I got loads of shots. Derek, he was on the deck of a ship a lot nearer. Those men, they had to sit with their backs to the horizon, cover their faces with their hands. Derek said he could see all his finger bones glowing through his hand. Like they was burning."

This echoes many of the first-hand accounts of those who were there, especially the bit about the finger bones. For example, Ron Watson – then a 17-year-old British soldier deployed with the Army Royal Engineers – told The Conversation that he was struck by an unbelievably bright light: "I had my back to the explosion. My eyes closed with my hands covering them. I clearly saw the bones in my hand, just like you see them if you look at the results of an X-ray."

Similarly, Bob Fleming (then 24, and wearing flip flops with a t-shirt and shorts) told the BBC: "It was awe-inspiring, like another sun hanging in the sky... we had no protective clothing. We were guinea pigs. It was so bright I could see the bones in my hands with my eyes closed. It was like an X-ray."

Terry Quinlan (19 years old at the time) said he witnessed five blasts in 1958: "We had no protective clothing, I wasn't even issued a pair of sunglasses. We were just told to assemble, sit down and to put our fists in our eyes. The officers were not with us, they had protective clothing and bunkers elsewhere... we were pushed along the beach by the blast and people's backs were scorched."

While they had their backs to the blast when the explosion took place, many were then ordered to turn around and look directly at the mushroom cloud as it grew into the sky.

Inhabitants of the islands – of whom there were several hundred – also recalled being taken offshore by boats and cargo ships during tests, or (on one occasion) being gathered on a tennis court covered by a tarpaulin.

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Did the nuclear tests lead to cancers and deformities?

In the short term, exposure to a nuclear blast can cause radiation poisoning (also known as radiation sickness). Symptoms are usually nausea, vomiting, and a loss of appetite; in Call the Midwife, Dr Turner realises that the British servicemen mistakenly thought they had food poisoning from eating bad fish, when they were suffering from the effects of radiation poisoning.

In the long term, exposure to high doses of radiation can cause other very serious effects on the body, such as cancer or leukaemia. Ionising radiation can even cause DNA damage, which can be passed down to children and grandchildren.

Many servicemen and islanders who were present at Christmas Island from 1957 to 1962 later reported severe health problems, which they attributed to the nuclear bomb tests – from cancers to organ failure. Some said they experienced fertility issues and problems having children; when they did have children and grandchildren, they reported high incidences of birth defects, hip and kneecap deformities, skeletal abnormalities, spina bifida, scoliosis, and limb abnormalities.

The British Nuclear Test Veterans Association (BNTVA) was formed in 1983 to represent and support these men. Despite dwindling numbers of survivors, it remains active in campaigning for its members and their descendants.

Inhabitants of the islands also reported similar problems. Those living there at the time have said they became unwell after consuming food such as coconuts and fish, which was contaminated by the successive nuclear blasts. Health problems among those inhabitants and their families could also be attributable to the hydrogen bomb tests.

In 2019, MP Carol Monaghan highlighted the case of William Caldwell, who was on a ship approximately 12 miles from the detonation site and who (like Call the Midwife's Derek) consumed fish after the blast: "After the cloud went up, a black rain fell, followed by dead fish floating to the surface of the water. The crew netted those fish and ate them, delighted by the convenience of their bounty and unaware of the risks." Caldwell later experienced severe stomach problems, and had to have half of his stomach removed.

What does the Ministry of Defence say?

The link between the nuclear testing and health problems is contested by the Ministry of Defence, which maintains that British servicemen and local people were not exposed to unsafe levels of radiation.

In a 2019 parliamentary debate, the Under-Secretary of State for Defence said: "Protection, health and welfare of all those involved in the tests were in place, and that is confirmed by well documented safety measures and monitoring during the tests. To date, there is no expert evidence of excess illness or mortality among nuclear test veterans in general that could be linked to their participation in the tests."

Because of military secrecy, in the 1950s and early 1960s there were no long-term health studies of nuclear test veterans. Those who were present during the tests at Christmas Island were not given medical examinations when they left, and their health was not studied after they finished their service.

In 1983, the Ministry of Defence did commission a study of more than 21,000 veterans, but – while the study found a slightly elevated risk of leukaemia – it actually concluded that the veterans had experienced no ill health as a result of their nuclear exposure. That said, not everyone accepted the results of that study.

The UK has not provided any compensation to its bomb test veterans. A Supreme Court case in 2012 ruled against a group of veterans who had made a claim for compensation, with the Justices saying that the veterans would face great difficulty proving a link between their illnesses and the tests.

In 2018, Brunel University in London started a three-year genetic study of 50 veterans and their families, aimed at finding out whether there is "evidence of genetic damage as a consequence of possible exposure to ionising radiation at nuclear weapons test sites in the 1950s and 1960s." Results are expected to be published in mid-2021.

Call the Midwife continues on Sundays at 8pm on BBC One. While you're waiting, take a look at the rest of our Drama coverage, or check out our TV guide.