Very little is known in the UK about the experiences of women service personnel and veterans (those who have left military service) with regards to military sexual trauma (MST) (sexual harassment and/or assault that occurs in military service), or sexual harassment and assault that happens outside of the military, and the resulting impact on their mental health. Whilst sexual assault and harassment can happen to both men and women, US military research has found that women report this at far higher levels, experience significant barriers to seeking help and support, and have resulting long-term mental health problems such as posttraumatic stress disorder (PTSD). In the UK, a research review in 2021 titled, ‘We Also Served’, identified MST as a top priority for research. Additionally, a recent parliamentary Defence Select Committee investigation in 2021 tasked with examining women’s experiences of service identified many instances of ‘unacceptable behaviours’ targeted at women that ranged from a culture of masculine banter to sexual harassment and rape. Using data and recruitment from a UK cohort study that has assessed the health and wellbeing of UK Armed Forces who deployed to Iraq and Afghanistan since 2003, this project will use both surveys and interviews to assess the levels and experiences of UK women service personnel and veterans that report sexual harassment and/or sexual assault. The study will examine whether these events happened during their military service, what the impact is on their mental health and what the risk factors are in relation to poor mental health. The study will also discuss with women who have and have not experienced sexual harassment/assault about their perceptions and experiences of military culture and their work environment in-service in relation to ‘unacceptable behaviours’ such as sexualised banter or knowledge of sexual harassment/assault. The study will further investigate any barriers to help-seeking and will work with women, the military and NHS providers of treatment and support services to improve the design of services so they are tailored to women’s needs. This project will give voice and understanding to a previously underserved group of women, connect its findings to influence improvements in practical policy and service design, and offer evidence that can be utilised in other occupational fields where women are a minority, therefore extending impact beyond this project.