The British Army will have the "biggest adjustments to make" following the release of the Defence Command Paper, defence analyst Professor Michael Clarke has told Forces News.
The document highlights in which ways all three services will adapt their roles and strategies following the publication of the Integrated Review.
One of the changes is the Army's regular force being reduced by thousands of personnel within the next four years.
According to the latest data, the service currently has just over 103,000 trained personnel in total, including more than 76,000 regular soldiers – it represents a shortfall based on the total target of 112,000 personnel for the entire Army.
The 2015 National Security Strategy and Strategic Defence and Security Review (SDSR) stated ambitions "to not reduce the [regular] Army to below 82,000".
"The people with the biggest adjustment to make are undoubtedly the Army," Professor Michael Clarke said.
He added: "The Army won't just be smaller, but [it] will be reorganised in some pretty big ways."
The United Kingdom already has one of the smallest armies among major European nations.
An announcement made on Monday by Defence Secretary Ben Wallace said it will be reduced to 72,500 by 2025.
Prof Clarke said the Ministry of Defence (MOD) are "taking a bet" as they aim to "transform the Army" so that it can be "much more lethal, much more agile, much more mobile".
However, the defence analyst also stressed that the British Army "will have to re-work itself in some pretty fundamental ways to make all this operate properly".
Asked how he believes the announcements made on Monday are being perceived internationally, Prof Clarke remarked that "there is some worry amongst our friends and allies".
He said: "On the one hand they applaud the idea that we're being bold enough to try to make the technological leap... but against that, they do worry about this question of size.
"If we're so small as a nation in terms of our Armed Forces, can we really make a strategic difference?"
The defence expert added that while changes proposed in the Defence Command Paper can make the UK "welcome" in the international sphere, but he added: "Being welcome in a coalition is not the same as making a strategic difference".
"Individual serving men and women should be reassured there are no redundancies involved in this," Boris Johnson said.
The same point was also echoed by the Defence Secretary as he proceeded with his announcement in the House of Commons, which stated that the Army numbers reduction will "not require redundancies".