The Royal Netherlands Air Force and the Royal Norwegian Air Force have developed an Electronic Learning Environment for F-16 maintenance training, which takes full advantage of advanced learning technology. Central in the blended learning environment is a course management system (CMS). We will discuss the differences between closed / commercial software source (CSS) and open source software (OSS) for e-learning systems. It appears that OSS has some distinct advantages, the most important are availability of source code, supplier independency and flexibility and freedom. Both Air Forces have chosen to start with a try-out with an open source CMS called Moodle. We have distinguished five key issues to be tested in the try-out. The first issue is related to security: 'Is it possible to provide military maintenance training safely on the Internet?' The second issue is related to use of different learning models: 'Is it possible to develop and implement both individual training and team training by means of the Moodle CMS? The third issue is related to the development of didactical templates: 'Is it possible to use an open, constructivist approach in which learning tasks are central to learning, and still use pre-structured templates to promote efficient content development?. The fourth issue is related to the integration of different training media in the design: 'Is it possible to combine traditional e-learning modules with the Air Forces synthetic F16 maintenance environment?' The fifth issue is related to classroom training and learning on demand. Is it possible to use Moodle as a delivery tool for new content? We will describe the process and outcomes of this try-out, both for a well-controlled laboratory setting as well as for a real situation with military personnel abroad (for instance Afghanistan).