Controlled natural language (CNL) has great potential to support human-machine interaction (HMI) because it provides an information representation that is both human readable and machine processable. We investigated the effectiveness of a CNL-based conversational interface for HMI in a behavioral experiment called simple human experiment regarding locally observed collective knowledge (Sherlock). In Sherlock, individuals acted in groups to discover and report information to the machine using natural language (NL), which the machine then processed into CNL. The machine fused responses from different users to form a common operating picture, a dashboard showing the level of agreement for distinct information. To obtain information to add to this dashboard, users explored the real world in a simulated crowdsourced sensing scenario. This scenario represented a simplified controlled analog for tactical intelligence (i.e., direct intelligence of the environment), which is key for rapidly planning military, law enforcement, and emergency operations. Overall, despite close to zero training, 74% of the users inputted NL that was machine interpretable and addressed the assigned tasks. An experimental manipulation aimed to increase user-machine interaction, however, did not improve performance as hypothesized. Nevertheless, results indicate that the conversational interface may be effective in assisting humans with collection and fusion of information in a crowdsourcing context.