At a recent Critical Mass Community session, Colonel Simon Farebrother MC and Dr Catherine Smith, SO1 Senior Occupational Psychologist, shared the findings of the British Army’s Critical Mass trial at the Royal Military Academy Sandhurst, which increased the proportion of female Officer Cadets in selected platoons to around 30%. The trial offers a powerful example of how targeted, evidence-based interventions can drive meaningful cultural change within complex organisations.
Why change was needed.
Sandhurst has long been recognised for its rigorous and demanding officer training. However, like many long-established institutions, elements of its culture had not evolved at the same pace as the organisation itself.
The Critical Mass trial was rooted in a service inquiry recommendation to review the culture of the Commissioning Course, with a particular focus on trainee experience and female integration.
Alongside this, qualitative feedback from officer cadets highlighted recurring issues such as isolation, low-level sexism, and feeling like a ‘lesser member of the platoon’ when women were present in small numbers.
Historically, Sandhurst had moved from single-sex training to full integration with only two or three women in each platoon. This model, while well-intentioned, did not always create an inclusive or supportive environment.
The critical mass approach
The trial evaluated a simple but impactful idea: that by increasing the proportion of female officer cadets in selected platoons to around 30%. individuals would no longer be seen as ‘tokens’ and would be better able to influence group dynamics.
Importantly, the trial required no changes to training standards, course content, or selection processes. The only variable adjusted was the composition of platoons making it a low-cost intervention with minimal disruption.
This work also sat alongside broader efforts to reset organisational culture at Sandhurst, including changes to alcohol policy, clearer codes of conduct, and mechanisms to address unacceptable behaviours.
What the evidence showed
The trial was evaluated through a combination of surveys and focus groups, measuring areas such as psychological safety, social support, organisational trust, engagement, and resilience.
The results were encouraging:
Social support and organisational trust increased across all trial cohorts.
Psychological safety and peer support improved in most cohorts.
Job satisfaction and resilience showed positive, if more limited, increases
Interestingly, when results were analysed by gender, many of these improvements were most visible among male cadets. This reinforces a key takeaway that improving culture benefits everyone, not just a particular group.
One of the most compelling findings came from the broader Officer Cadet Survey data. Among female cadets:
Those reporting fair treatment increased from 78% to 92%.
Those reporting training conducted without harassment increased from 90% to 98%.
These shifts indicate a significant improvement in lived experience, bringing outcomes for women in line with their male peers.
What changed in practice
Qualitative feedback provided important context behind the data.
With a greater number of women in each platoon, cadets reported feeling more supported and less isolated. The increased representation reduced the pressure of being highly visible and enabled individuals to contribute more confidently.
The impact extended beyond gender. Both men and women described improved communication, greater mutual understanding, and a more balanced team dynamic often characterised by less aggression and more open dialogue.
Crucially, the trial also disrupted patterns of stereotyping. With only one or two women in a group, behaviours could be generalised unfairly. A larger, more diverse group encouraged cadets to assess each other as individuals, strengthening overall cohesion.
Lessons learned
The trial was not without its challenges or criticisms. Questions were raised about whether the model reflects the reality of the Field Army, and whether it risks creating an environment that cannot be sustained later in careers.
However, a key principle of the work was to optimise the training environment for learning and development rather than replicating every aspect of future conditions. The aim was to create the best possible foundation for individuals to succeed.
The most important insight is a shift in perspective: rather than asking how to ‘fix’ underrepresented groups, the focus should be on shaping systems and cultures to enable everyone to thrive.
A step forward
While not positioned as a complete solution, the Critical Mass trial demonstrates what can be achieved through thoughtful, evidence-led change. The approach is now being continued as standard practice at Sandhurst reflecting confidence in both its impact and its practicality.
For the defence community more broadly, this work offers a clear message: meaningful cultural change does not always require large-scale transformation. Sometimes, small adjustments grounded in data and driven by intent can create lasting impact.