The atmospheres of US Navy Submarines are unique closed environments in which sailors both live and work for extended periods. Although this atmosphere is continuously monitored with a real-time, mass spectrometer-based Central Atmosphere Monitoring System (CAMS), the ability to measure trace constituents is limited. The identity, concentrations and distributions of trace constituents have been studied more exhaustively, in some cases for as long as the duration of a patrol, using conventional active air sampling methods such as passivated stainless steel canisters and solid sorbent tubes. The results from these studies indicate that trace constituents are generally present at concentrations well below levels that would present health concerns. However, these studies also show that there is a fairly wide variation in such levels over time, operational conditions, submarine and class of submarine. Moreover, these studies have been limited in number and, most importantly, represent a very small percentage of sampling time relative to the actual amount of time a sailor is exposed to the atmosphere. Consequently, our understanding of the nature, constituents and variation of the atmosphere aboard submarines is limited. The availability of an accurate picture of any submarine's atmosphere at any time would be invaluable from both health and engineering perspectives. To address this problem, the Royal Navy conducts weekly retrospective sampling, on granulated activated carbon on each of its submarines. The logistics of conducting such sampling on the larger US fleet are daunting, and have led us to explore alternative approaches employing passive monitoring. We have investigated the deployment of passive monitoring badges, normally used for industrial hygiene monitoring in the 8-hour world, for the low-level (part-per-billion) long term (28 days) measurement of trace constituents such as formaldehyde, benzene, ozone and toluene in submarines. This work has involved long-term laboratory validation of the monitors, validation of the monitors on board submarines, and measurements of trace constituents aboard submarines. The use of simple, relatively inexpensive diffusive sampling monitors allows for measurements to be made at multiple points within the submarine, over extended periods of time, with minimal impact on the crew's operations, and by using the ships' corpsman. Diffusive sampling monitors provide important information that complements the information provided by real-time monitoring.