Number of personnel in UK armed forces 1900-2020

In 2020 there were over 145 thousand personnel serving in the British Armed Forces, the second-fewest of any year since 1900, with just 144 thousand serving in 2019. In the first half of the twentieth century, there are two huge spikes in the number of personnel which represent the final years of World War One and World War Two, with the British Armed Forces numbering 4.58 million and 4.69 million in 1918 and 1945 respectively. Ever since 1945 the size of the UK Armed Forces has been in almost constant decline, with the noticeable exception of the early 1950s, where Britain's armed forces increased by almost 200 thousand because of the Korean War.

The winds of change

There are several reasons why the number of personnel in Britain’s armed forces has declined. Britain is involved in a far fewer conventional military conflicts today than it was in the past. As the size of Britain’s empire declined rapidly after 1945, so too did the its global military commitments. There are also more recent developments such as the UK government’s Strategic Defence and Security Review of 2010, which outlined personnel would be cut throughout the 2010s in order to modernize the UK’s armed forces.

Branches of the UK military

There are four branches of the UK armed forces, the British Army, the Royal Navy, the Royal Air Force, and the Royal Marines. Of the 149 thousand people serving in the UK’s armed forces in 2021, over half of them were in the British Army, which had 82 thousand personnel. The next largest branch was the RAF at 33.2 thousand, followed by the Royal Navy at 27.21 thousand, and finally the Royal Marines, which was the smallest branch in terms of personnel, at 6.64 thousand.