At the time of decimalisation in 1971, the United Kingdom Crown coin (equal to 5 shillings) was redenominated as a 25p coin and pieces struck prior to 1990 - all the way back to 1818 - continue to be legal tender for that amount. The old denomination had been a regular circulating coin in the 19th century, but in the 20th century it became more of a commemorative denomination.
The Royal Mint continued issuing commemorative coins in the same format - using the traditional coin dimensions, but in copper-nickel. These were initially also denominated as 25 pence but the "Crown" was changed in 1990 to a commemorative £5 (five pound) coin, having the same dimensions and weight but with a face value twenty times as great.
The denomination is used to mark special occasions, usually royal in theme, rather than for use in general circulation. Although not circulating, these coins are legal tender.
This commemorative £5 Crown-sized coin was issued as part of a six-coin set of similar coins commemorating the Centenary of the First World War; the set itself is the fourth part of a series of sets issued over several years. This coin highlights the horrors of the Gas Warfare during the war.
Although the Hague Convention of 1899 had banned "the diffusion of asphyxiating or deleterious gases", both the French and German armies employed tear gas and other non-lethal chemicals during 1914 and 1915. The unpredictable nature of gas warfare was highlighted on 25 September 1915 at the Battle of Loos, when clouds of chlorine gas discharged from cylinders by the British Army blew back over their own trenches. As a result, gas shells for the artillery were developed to provide a far more reliable and accurate method of delivery than cylinders. As the war progressed, increasingly lethal gases were developed - including mustard gas, first used by the Germans at Ypres in July 1917.
Gas warfare had a far greater psychological impact than a military one. It accounted for only 3% of all casualties on the battlefield but many more men suffered long-term illness, debility and premature death after the war had ended. Widespread horror and public revulsion at the use of gas and its consequences led to far less use of chemical weapons by combatants during World War Two.
The coin was designed by Edwina Ellis:
“Gas masks and their purpose reveal so much of the First World War story and its tragedy but it was a real challenge to capture the menace of gas on a coin’s small surface. The mask in my design is based on one I saw at the Chalk Valley History Festival, where an anonymous ex-soldier associated with Help for Heroes gave me valuable assistance. He was dressed in First World War soldier’s uniform and helped by putting on his gas mask and posing for me to take photographs.
This model of mask had a separate charcoal filter-bag joined at the mouth by a hose, this and the mica-covered eyepieces made breathing and visibility a bit easier for the soldiers; while adding a graphic spookiness. The design shows an ordered, fanned pattern of gas particles doing their horrible damage.”
The coin’s edge lettering, "GUTTERING CHOKING DROWNING", is taken from "Dulce et Decorum Est", the famous poem by Wilfred Owen.
The coin was issued in Proof FDC, in sterling silver and in a gold, both in sets only and not issued individually. | 
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