U.S. Navy personnel who work on submarines are in an enclosed and isolated environment for days or weeks at a time when at sea. To protect workers from potential adverse health effects due to those conditions, the U.S. Navy has established exposure guidance levels for a number of contaminants. In this latest report in a series, the Navy asked the National Research Council (NRC) to review, and develop when necessary, exposure guidance levels for 11 contaminants. The report recommends exposure levels for hydrogen that are lower than current Navy guidelines. For all other contaminants (except for two for which there are insufficient data), recommended levels are similar to or slightly higher than those proposed by the Navy. The report finds that, overall, there is very little exposure data available on the submarine environment and echoes recommendations from earlier NRC reports to expand exposure monitoring in submarines.