Image caption This dog was treated by a vet, but many were put down at the outbreak of WWII

At the beginning of World War II, a government pamphlet led to a massive cull of British pets. As many as 750,000 British pets were killed in just one week. This little-discussed moment of panic is explored in a new book.

The cull came as the result of a public information campaign that caused an extraordinary reaction among anxious Britons.

In the summer of 1939, just before the outbreak of war, the National Air Raid Precautions Animals Committee (NARPAC) was formed. It drafted a notice - Advice to Animal Owners.

The pamphlet said: "If at all possible, send or take your household animals into the country in advance of an emergency." It concluded: "If you cannot place them in the care of neighbours, it really is kindest to have them destroyed."

The advice was printed in almost every newspaper and announced on the BBC. It was "a national tragedy in the making", says Clare Campbell, author of new book Bonzo's War: Animals Under Fire 1939 -1945.

Campbell recalls a story about her uncle. "Shortly after the invasion of Poland, it was announced on the radio that there might be a shortage of food. My uncle announced that the family pet Paddy would have to be destroyed the next day."

After war was declared on 3 September 1939, pet owners thronged to vets' surgeries and animal homes.

Image caption An RAF serviceman delivers a stray to Battersea

"Animal charities, the PDSA, the RSPCA and vets were all opposed to the killing of pets and very concerned about people just dumping animals on their doorsteps at the start of the war," says historian Hilda Kean.

Battersea Dogs and Cats Home opened its doors in 1860 and survived both wars. "Many people contacted us after the outbreak of war to ask us to euthanise their pets - either because they were going off to war, they were bombed, or they could no longer afford to keep them during rationing," a spokesman says.

"Battersea actually advised against taking such drastic measures and our then manager Edward Healey-Tutt wrote to people asking them not to be too hasty."

But Campbell cites an Arthur Moss of the RSPCA who, "gloomily pronounced that the primary task for them all would be the destruction of animals".

In the first few days of war, PDSA hospitals and dispensaries were overwhelmed by owners bringing their pets for destruction. PDSA founder Maria Dickin reported: "Our technical officers called upon to perform this unhappy duty will never forget the tragedy of those days."

It was one of things people had to do - evacuate the children, put up the blackout curtains, kill the cat Hilda Kean

In Memoriam notices started to appear in the press. "Happy memories of Iola, sweet faithful friend, given sleep September 4th 1939, to be saved suffering during the war. A short but happy life - 2 years, 12 weeks. Forgive us little pal," said one in Tail-Wagger Magazine.

The first bombing of London in September 1940 prompted more pet owners to rush to have their pets destroyed.

Many people panicked, but others tried to restore calm. "Putting your pets to sleep is a very tragic decision. Do not take it before it is absolutely necessary," urged Susan Day in the Daily Mirror.

But the government pamphlet had sowed a powerful seed.

"People were basically told to kill their pets and they did. They killed 750,000 of them in the space of a week - it was a real tragedy, a complete disaster," says Christy Campbell, who helped write Bonzo's War.

Historian Hilda Kean says that it was just another way of signifying that war had begun. "It was one of things people had to do when the news came - evacuate the children, put up the blackout curtains, kill the cat."

It was the lack of food, not bombs, that posed the biggest threat to wartime pets. There was no food ration for cats and dogs.

Image caption As war approached, families increasingly worried about feeding their animals

But many owners were able to make do. Pauline Caton was just five years old at the time and lived in Dagenham. She remembers "queuing up with the family at Blacks Market in Barking to buy horsemeat to feed the family cat".

The Duchess of Hamilton, 1878-1951 Nina Mary Benita Douglas-Hamilton, notable animal rights campaigner

Established animal sanctuary in a heated aerodrome in Ferne during war

Founded Scottish Society for Prevention of Vivisection in 1911 The Duchess at the National Portrait Gallery

And even though there were just four staff at Battersea, the home managed to feed and care for 145,000 dogs during the course of the war.

In the middle of the pet-culling mayhem, some people tried desperately to intervene. The Duchess of Hamilton - both wealthy and a cat lover - rushed from Scotland to London with her own statement to be broadcast on the BBC. "Homes in the country urgently required for those dogs and cats which must otherwise be left behind to starve to death or be shot."

"Being a duchess she had a bit of money and established an animal sanctuary," says historian Kean. The "sanctuary" was a heated aerodrome in Ferne. The duchess sent her staff out to rescue pets from the East End of London. Hundreds and hundreds of animals were taken back initially to her home in St John's Wood. She apologised to the neighbours who complained about the barking.

But at a time of such uncertainty, many pet owners were swayed by the worst-case scenario.

More on WWII from BBC History World War II brought many changes to the lives of Britons. To ensure fair distribution of goods and food, the Ministry of Food issued ration books to every person during the war. The sustained German bombing - known as the Blitz - of London and other major cities caused many civilian casualties and deaths. Approximately three million people were evacuated from towns and cities that were in danger of being bombed by enemy aircraft.

"People were worried about the threat of bombing and food shortages, and felt it inappropriate to have the 'luxury' of a pet during wartime," explains Pip Dodd, senior curator at the National Army Museum.

"The Royal Army Veterinary Corps and the RSPCA tried to stop this, particularly as dogs were needed for the war effort."

Ultimately, given the unimaginable human suffering that followed over the six years of the war, it is perhaps understandable that the extraordinary cull of pets is not better known.

But the episode brought another sadness to people panicked and fearful at the start of hostilities.

The story is not more widely known because it was a difficult story to tell, says Kean.

"It isn't well known that so many pets were killed because it isn't a nice story, it doesn't fit with this notion of us as a nation of animal lovers. People don't like to remember that at the first sign of war we went out to kill the pussycat," she says.

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Bonzo's War: Animals Under Fire 1939 -1945 is written by Clare Campbell with Christy Campbell.