This article was first published in the November 2011 issue of BBC History Magazine

In the autumn of 1917, a notice appeared on the walls of classrooms and scout huts across Britain: “Groups of scholars and boy scouts are being organised to collect conkers… This collection is invaluable war work and is very urgent. Please encourage it.”

It was never explained to schoolchildren exactly how conkers could help the war effort. Nor did they care. They were more interested in the War Office’s bounty of 7s 6d (37.5p) for every hundred weight they handed in, and for weeks they scoured woods and lanes for the shiny brown objects they usually destroyed in the playground game.

The children’s efforts were so successful that they collected more conkers than there were trains to transport them, and piles were seen rotting at railway stations. But a total of 3,000 tonnes of conkers did reach their destination – the Synthetic Products Company at King’s Lynn – where they were used to make acetone, a vital component of the smokeless propellant for shells and bullets known as cordite.

Cordite had been used by the British military since 1889, when it first replaced black gunpowder. It consisted chiefly of the high-explosives nitroglycerine and nitrocellulose (gun-cotton), with acetone playing the key role of solvent in the manufacturing process.

Prior to the First World War, the acetone used in British munitions was made almost entirely from the dry distillation (pyrolysis) of wood. As it required almost a hundred tonnes of birch, beech or maple to produce a tonne of acetone, the great timber-growing countries were the biggest producers of this vital commodity, and Britain was forced to import the vast majority of its acetone from the United States.

An attempt to produce our own acetone was made in 1913 when a modern factory was built in the Forest of Dean. But by the outbreak of war in 1914, the stocks for military use were just 3,200 tonnes, and it was soon obvious that an alternative domestic supply would be needed. This became even more pressing during the spring of 1915 when an acute shortage of shells – the so-called ‘shell crisis’ – reduced some British guns to firing just four times a day.

The British government’s response was to create a dedicated Ministry of Munitions, run by the future prime minister David Lloyd George. One of Lloyd George’s first initiatives was to ask the brilliant chemist Chaim Weizmann of Manchester University if there was an alternative way of making acetone in large quantities. Weizmann said yes.

Developing the work of Louis Pasteur and others, Weizmann had perfected an anaerobic fermentation process that used a highly vigorous bacterium known as Clostridium acetobutylicum (also known as the Weizmann organism) to produce large quantities of acetone from a variety of starchy foodstuffs such as grain, maize and rice. He at once agreed to place his process at the disposal of the government.

In May 1915, after Weizmann had demonstrated to the Admiralty that he could convert 100 tonnes of grain to 12 tonnes of acetone, the government commandeered brewing and distillery equipment, and built factories to utilise the new process at Holton Heath in Dorset and King’s Lynn in Norfolk. Together they produced more than 90,000 gallons of acetone a year, enough to feed the war’s seemingly insatiable demand for cordite. (The British army and Royal Navy, alone, fired 248 million shells from 1914 to 1918.)

But by 1917, as grain and potatoes were needed to feed the British population, and German U-boat activity in the Atlantic was threatening to cut off the import of maize from the United States, Weizmann was tasked to find another supply of starch for his process that would not interfere with the already limited food supplies.

He began experimenting with conkers, aware that they grew in abundance across the country, and found that the yield of acetone was sufficiently high to begin production. This, in turn, prompted the nationwide appeal for schoolchildren to collect the conkers and hand them in.

1st October 1926: Boys in their uniform shorts and long socks conker fighting in the conker season in Hornsey, London, 1926. (Photo by Fox Photos/Getty Images)The government was determined not to reveal the real reason for the great chestnut hunt of 1917 in case the blockaded Germans copied their methods. The only official statement was printed in The Times on 26 July 1917.

It read: “Chestnut seeds, not the green husks, are required by the Government for the Ministry of Munitions. The nuts will replace cereals which have been necessary for the production of an article of great importance in the prosecution of the War.”

When questions were asked in the House of Commons, the veiled response was that the conkers were needed for “certain purposes”. So suspicious did some members of the public become that they accused the government of using voluntary labour for private profit.

The actual production of acetone from conkers was, despite Weizmann’s assurances, never that successful. Teething problems meant the manufacturing process did not begin in the King’s Lynn factory until April 1918, and it was soon discovered that horse chestnuts did not provide the yields the government had hoped for. Production ended after just three months.

So did conkers really help to win the war? They played their part, certainly, even if their role was more walk-on than centre stage. The real star of the show was Chaim Weizmann, whose brilliant solution to the acetone shortage – using a variety of natural products from maize to conkers – helped to solve the shell crisis and get Britain’s guns firing again.

A leading Zionist, Weizmann was rewarded for his vital contribution to Britain’s war effort when the cabinet – prompted by Lloyd George, prime minister since late 1916 – approved the signing of the Balfour Declaration on 2 November 1917. Taking the form of a letter from Arthur Balfour, the foreign secretary, to Lord Rothschild, a leading British Jew, it promised government support “for the establishment in Palestine of a national home for the Jewish people”, and was the first step on the long road to Israeli statehood.

When the state of Israel was finally established in 1948, Weizmann became its first president. For good or ill, conkers were partly responsible.

Saul David is a historian, broadcaster and author, whose books include War: From Ancient Egypt to Iraq (Dorling Kindersley, 2009).