The development of mobile health applications (apps) is growing exponentially. Alcohol reduction apps can break down perceived barriers of seeking help for alcohol misuse, potentially making them more appealing than face-to-face methods. App usability is therefore essential in supporting individuals misusing alcohol. Alcohol misuse is common in the UK Armed Forces, therefore smartphone-based alcohol interventions could be valuable for this population. The aim of this pilot study was to assess the usability of Drinks:Ration, an alcohol reduction app for military veterans. Participants downloaded and used Drinks:Ration for 14-days (n = 16), completed a usability questionnaire (n = 14; 88%) and a semi-structured interview (n = 12; 75%). The mean usability score across all measures was 6.09 (SD 1.37), out of 7, indicating good usability. Three core themes were identified: simplicity; appropriateness for veterans; and engagement. Drinks:Ration was a usable app for veterans to monitor their alcohol consumption. Veteran users were more critical than expert users about the usefulness of the app. Feedback was incorporated into the app, where possible, to improve usability. Improvements included adding extra drink options, removing device notification sounds and adding a pop-up to each page which provides information about the features of the app on first use.