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 commemorates the Sopwith Camel airplane.
The Sopwith Camel was a British First World War single-seat biplane fighter aircraft that was introduced on the Western Front in 1917. It was developed by the Sopwith Aviation Company as a successor to the Sopwith Pup and became one of the best known fighter aircraft of the Great War.
The Camel was powered by a single rotary engine and was armed with twin synchronized Vickers machine guns. Though difficult to handle, it was highly manoeuvrable in the hands of an experienced pilot, a vital attribute in the relatively low-speed, low-altitude dogfights of the era. In total, Camel pilots have been credited with downing 1,294 enemy aircraft, more than any other Allied fighter of the conflict. Towards the end of the First World War, the type also saw use as a ground-attack aircraft, partly because the capabilities of fighter aircraft on both sides advanced rapidly and left the Camel somewhat outclassed.
Edwina Ellis has captured the innovative structure of the Sopwith Camel in her design:
“At the beginning of their technological development, planes had a touching naivety to a twenty-first century gaze. I often felt frivolous examining objects of such importance to the survival of their users. I sought the help of several experts to ensure my design was accurate. I found that the hole in the top of the fuselage was for pilots to fire the Vickers guns through. The early planes were so vulnerable and slight, I could understand why early pilots’ slang for their machines was a "kite" - even featuring elastic bands and canvas-covered, bicycle style wheels. This was why early existent plane wheels are often wobbly-looking on their axles, but as my coin version depicted the plane as a newly-invented, unscathed Sopwith, I opted to straighten the wheels.”
The edge lettering "IRRITATUS LACESSIT CRABRO" translates to "The hornet attacks when roused". This motto appears on the badge of the 213 Squadron of the Royal Naval Air Service.
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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