Mind wandering is common during daily activities and is even more prevalent under stressful conditions, which could lead to lapses in attention and poor performance. Newly recruited military personnel who undergo demanding training often experience high levels of stress. It is therefore imperative to find ways to foster mental health and avoid performance deterioration related to mind wandering in times of intense military training. This feasibility study investigated the effectiveness of an established low-dose mindfulness-based intervention (MBI), called Mindfulness-based Attention Training (MBAT), on mind wandering, attentional performance, and well-being, delivered by a facilitator who was taught how to deliver MBAT. A sample of newly recruited Royal New Zealand Navy (RNZN) Junior Officers (n = 17) undergoing demanding training participated in the 8-week long MBI with one weekly contact session. Measures of well-being and the Sustained Attention to Response Task (SART) were completed 4 weeks prior to the MBAT, at the start of the MBAT, at the end of the MBAT and 4 weeks after completion of the MBAT. Results suggest that MBAT might protect from performance decline during intense training and enhance levels of well-being at follow-up. These findings highlight the valuable role of mindfulness as a component in military training.