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The Future Soldier warfighting structure stands as an impediment to the British Army attaining mass, with reservist unit training withering.

With near-peer threats and stiff economic challenges, 2025's Strategic Defence Review has hard balance to find if it is going to provide a credible Land force, but such a balance has been struck before.

The British Army needs depth to be sustainable in war: both a second echelon to follow close behind the first, and structures to generate a third and subsequent ones. The Strategic Defence Review (SDR) and the Treasury, despite the recent increased announcement in spending, are unlikely to both fund more regular troops for a second echelon and maintain the equipment programme and extra munitions required for modernisation. Army Reserve units and formations can provide the cost-effective additional mass to expand the army in war and deliver that second echelon.

The Strategic Reserve can provide individual reinforcements but cannot grow the army with additional units. The current Future Soldier warfighting structure inhibits the ability of the Army Reserve to expand the British Army in war. This commentary looks to the last time a Defence Review had to balance ‘NATO First’ with modernising the army in fiscally challenging times, set against a peer-level threat in Europe. It illustrates how the British Army embraced their reserve forces to reorganise and modernise into an army that was sustainable, affordable and played a key role in successfully delivering deterrence.

The Current Demand for ‘Mass’

There has been much mention of ‘mass’ and the British Army, aligned to the SDR’s considerations. To be credible for high intensity warfighting experience from Ukraine suggests that the British Army will require access to more mass. Mass in these reports usually implies access to more numbers of people, more equipment and more munitions. However, the continuing financial pressures on UK Defence will likely prevent any significant increase to the numerical mass of full-time forces if it is to also provide the better firepower, enablement, readiness and resilience required. As a result, there has been more of an emphasis on the current force structure’s ability to successfully mass the effect of combat power through enhanced lethality delivered by modernisation, improved command and control, robotics and faster exploitation of information.

These enhancements are indeed important to win the first battle, especially for the UK’s medium sized army, but wars are rarely won by the first battle and peer-level opponents will return for a second round. It is important for an Army to retain enough people, equipment and munitions to deal with a wartime level of attrition and to continue to provide the range of capabilities to ensure it can at least take part in the second battle, and beyond. The Chief of Defence Staff Admiral Tony Radakin is correct that war in Europe is a remote chance but NATO’s land force sustainability is also important for keeping the odds low through deterrence. What balance of investments will deliver the optimum and sustainable British Army for its near-term readiness for warfighting?

In simple force development terms sustainable depth is attained through the provision of additional capability, such as follow-on echelons. The structural basis of capability in the British Army, as in most other armies, is the unit and the formation. Most nations cannot afford to have standing armies made up of the required number of trained and equipped units ready to fight large wars. Peacetime armies are limited in size by national budgets and as Andrew Sharpe points out must be ready to expand rapidly to cope with the heavier demands of war. Threats and tasks increase greatly in war, formations suffer attrition, units need to be replaced, areas of operation grow larger. The medium-sized British Army must be ready at the outset to have a structure, a second echelon, which can generate more formations and more units for war, or it risks becoming very small, very quickly.

The peacetime formed reserve units of the Ukrainian Army were vastly more effective than those units pulled together from scratch

The British Army has traditionally relied on part-time Army Reserve units, who train collectively in peacetime, to generate the second echelon additional units for the expansion of the British Army in war. As has been pointed out many times before this remains the most cost effective and most successful way to expand the British Army for war. Additional units cannot simply be conjured up at the start of a war from pools of individual reinforcements, let alone untrained wartime volunteers.

The necessity for a funded, equipped and trained Army Reserve in peacetime has been a key lesson from Ukraine and from our own history. The peacetime formed reserve units of the Ukrainian Army were vastly more effective than those units pulled together from scratch with little cohesion and very poor combat effectiveness. While Army Reserve units are not equivalent in capability to Regular units, history, and our allies performance, show they can provide a “good enough” contingent capability within a few weeks from mobilisation, for the focussed wartime missions they should be allocated. This provides mass and sustainability, to allow time for subsequent echelons to be generated.

Peacetime armies also need many individual reinforcements on wartime mobilisation. They are needed to fill inevitable peacetime gaps in both regular and reserve units and to bring all units up to a wartime strength, not needed in peace, to ensure units can cope with the rigours of war. Individual reinforcements are also needed to provide formations with a battle casualty replacement pool. The British Army has traditionally called back ex-Regulars (the Regular Reserve and those with liability for recall, now termed the Strategic Reserve) to provide most of these individual reinforcements.

Individual reinforcements by themselves do not expand the Army, since they do not provide additional units, but are vital for making units and formations more resilient. Under current legislation you cannot “grow” the Strategic Reserve. They are fixed by virtue of being ex-regular so as a regular force shrinks so will the Strategic Reserve since their numbers are determined by regular leavers. Historically the Army have also developed plans to scour their peacetime-only structures to deliver more regulars in war for the deployable forces.

This simple-to-understand system, where the Army Reserve expanded the British Army in war with additional units on mobilisation and where the Regular Reserves were called back to provide resilience through individual gap filling, lasted for over 100 years. It was far from perfect, had its bumps, but was reasonably affordable in times of financial difficulty and was relatively successful when it came to fighting actual large-scale war and deterring a cold one. Unfortunately, this system has been slowly abandoned by the British Army over the last 30 years and the British Army will struggle to expand and deliver the mass it seems to have on paper.

The Un-Expandable 'Future Soldier' British Army

It has been acknowledged that some part of the “Future Soldier” programme have not been ideal for the British Army. This is especially true for the Army Reserve. The Chief of Staff of Field Army wrote in 2023 that “Without the Army Reserve, any notion of maintaining the Army’s combat endurance beyond the first ‘thunderclap’ is fanciful”. Yet, the bulk of the fighting power of the Army Reserve is structurally tied up with that first ‘thunderclap’. Under Future Soldier, on mobilisation for war, the majority of Army Reserve units will provide up to 70% of the Army Reserve unit workforce to backfill the gaps in Regular Army units.

This Future Soldier backfill demand on the Army Reserve effectively removes the capacity of the British Army to rapidly expand on mobilisation and fundamentally undercuts the role of the Army Reserve to provide additional units for wartime. It also risks undermining the first echelon readiness, as Army Reserve personnel are at lower levels of readiness, and many could not deploy immediately with their combat formations without some additional training.

The traditional second echelon of the British Army, with up to 70 Army Reserve units on paper, is currently planned to be spent against the first echelon. The British Army has no depth. Meanwhile, the pool of individual Regular Reservists that traditionally provided a backfill function have been allowed to assume they will never be needed and despite repeated attempts, going back decades now, they have not yet been brought out of abeyance. I have previously written on why this has been culturally difficult for the British Army to achieve.

Future Soldier, building on the slow withering of Army Reserve unit training since the end of the Cold War, has created a British Army for war that is primarily based on its full-time Regular Army structure in peace. The privileging of the units of the first echelon to the detriment of second echelon Army Reserve unit capability is explainable given financial pressures, is culturally understandable, has been influenced by political aversion to honest discussions about the Army, and has happened before. It makes the British Army in war a potentially “first battle” winning organisation, if the logistic problems of deploying can be overcome, but at the risk of being small and fragile for actual war winning. It has stripped out the capacity of the army to expand rapidly and to be more sustainable in war. Future Soldier has created the best possible single echelon force.

Any first rate second echelon will be a very long time arriving under Future Soldier. Yet the British Army has enough Army Reserve units now to create a second echelon; it has chosen to disinvest in their collective capability. The current Future Soldier structure also makes the British Army relatively more expensive for the units and resultant capability it can deliver in war in comparison to our NATO allies armies. Our NATO allies, including those who are also expeditionary, such as the Americans, still rely on cost effective expansion from reserve units and those like the French are investing heavily in building more reserve units. The fundamental withering of British Army Reserve capability has happened at a period when UK Defence is under pressure to deliver more wartime Land Forces for NATO and now also for UK Home Defence.

Thankfully, there is now growing recognition that in order to sustain itself in a large-scale war the British Army’s “Reserve force will form our second echelon.” To do this it will need to use units from the Army Reserve and call upon individual reinforcements from its Regular Reserves. The SDR call for evidence indicated that Reserve capability is going to be an important factor in their thinking. They appear to have a desire to make more of the Army Reserve and the Regular Reserves. Without additional money this will involve tough choices and indications are that the Treasury will be hard pressed to provide much more for defence.

The early 1980’s saw a heightened peer-level threat from Eastern Europe leading to demands to improve the UK Land contribution to NATO

For the Army, various Defence Reviews have been in this space before – with regard to the poor and misunderstood state of reserves – and perhaps lessons can be drawn. The 2010 Strategic Defence and Security Review and resultant Future Reserves 2020 programme show parallels, but were focused on developing operational reserve forces for lower intensity warfare. The review with some striking similarity to today’s British Army is perhaps the radical 1981 UK Defence Review.

The 1981 Defence Review – NATO First, High Threat but Little Extra Money

The early 1980’s saw a heightened peer-level threat from Eastern Europe leading to demands to improve the UK Land contribution to NATO. There was also an increased threat to the UK Homeland. This was set against severe financial constraints on growing UK Defence spending, but with Conservative party election pledges to increase the offer to Defence and make up for a decade of retrenchment and shrinkage.

On attaining power in 1979, a generous pay offer from the new government had been given to Defence to try to improve retention in 1980 while still having to deal with severe in-year pressures to reduce costs and cancel expenditure from an over extended budget. A Defence review was called for to match ambition to the resources available. The review was to be focussed on a ‘NATO First’ strategy.

Like today, the British Army was not in the best state. Some claimed the Army had the most outdated equipment in NATO. The Army had begun a process of modernisation of its key equipment, but with poor morale personnel recruitment was poor and outflow high. A previous review saw the warfighting corps adopt a structure that was not optimal.

The Army also needed to become more sustainable for a more flexible NATO warfighting response. This would require increased stocks and increased mass. The British Army of 1981 did not have enough units on mobilisation to cover the requirements of a deployed