Number of personnel in UK armed forces 1900-2024

In 2024, there were 138,120 personnel serving in the British Armed Forces, compared with 142,0 in the previous year. In the first half of the twentieth century, there were two huge spikes in the number of personnel which represented 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 200,000 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 UK's 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 to modernize the UK’s armed forces. Recent geopolitical events such as Russia's invasion of Ukraine have, however, led to commitments from the UK government to spend more on defence, and possibly even a reversal of personnel cuts.

Branches of the UK military

There are three main branches of the UK armed forces, the British Army, the Royal Navy, the Royal Air Force, and the Royal Marines. Of the 138,120 people serving in the UK’s armed forces in 2024, over half of them were in the British Army, which had 75,320 personnel. The next largest branch was the RAF at 30,800, followed by the Royal Navy at 32,000 personnel. The average age for people serving in the armed forces was 31 in 2023, with the Royal Air Force having a slightly higher average age group than the other branches, at 33.