Several methods have been proposed to treat combat veterans with Posttraumatic Stress Disorder (PTSD). Still, a recent review reports on high drop-out and non response rates. This has motivated work in the design of a software application to support and increase the appeal of traditional face-to-face trauma-focused psychotherapy. The research followed a situated cognitive engineering approach, which included a domain analysis, scenarios and claims analysis based on experts reviews (N=10), user evaluations, and a case study. This resulted in the identification of nine core application functions: (1) provide a flexible way of storytelling, (2) provide a structured way of storytelling, (3) prevent losing track of changed and added events, (4) ensure patient trust, (5) ensure usage for therapists with different backgrounds, (6) ensuring awareness of treatment, (7) provide a personal approach, (8) prevent unexpected exposure to emotional material, (9) and ensure an appealing and motivating approach throughout the therapy. These functions formed the basis for the design of a military multi-modal memory restructuring (Military - 3MR) system, which focuses on restructuring and relearning of past events. The system allows the patient and therapist to visualize past events using personal photos, narrative text, online geographical maps, webcam snapshots, and patient created 3-D virtual worlds. Results of the usability evaluation (N=18) suggest key design features, such as the time line, content management, and the 3- D world editor, meet an acceptable perceived usability level. Results of a storytelling experiment (N=18) between telling an autobiographical story with or without the Military-3MR system found that with the system, time referencing and event description were more precise, and a smaller time period in the story was covered. In the case study, the veteran suffering from combat-related PTSD was pleased with the system and felt encouraged talking about past events.@en