This set contains five 50 pence coins carrying the reverse designs of commemorative 50 pence issued in earlier years and having military topics; all coins in the set are dated 2019, and are gold piedforts (double the thickness and weight of the gold proofs).
The Royal Mint says:
"This year marks 50 years since the 50p first entered circulation. Over the last 50 years, the coin has commemorated epic battles and acts of valour that changed the course of history. Following the launch of the 50p British Culture Set, our celebrations continue with this release which brings together five military themed designs in one curated set.
Struck in 22 carat gold and finished to Proof standard, coins commemorating the 950th anniversary of the Battle of Hastings, the 50th anniversary of D-Day and the 75th anniversary of the Battle of Britain are presented alongside two coins marking the 150th anniversary of the creation of the Victoria Cross medal, the ultimate award for gallantry. It is a fitting way to mark this landmark moment for one of our most iconic coins." | 
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