This article briefly discusses some of the selected open-source intelligence methods on the Internet, which may be utilised to support activities of the armed forces. The paper examines this issue in two particular dimensions. On the one hand, it overviews some of the most popular means allowing supporting conventional operations, for instance, by geolocating hostile military infrastructure or troops. On the other hand, it explores some of the selected methods allowing to support cyber warfare. It concludes that open-source intelligence offers increasing capabilities, for instance, in detecting targets for offensive cyber operations or geolocating hostile troops. Nevertheless, it also has considerable limitations, particularly in terms of susceptibility to disinformation.