Early submarines relied on white mice instead of electronic sensors to detect dangerous leaks of carbon monoxide and other toxic gases while trapped deep underwater.

A closer look

Early submarines relied on white mice instead of electronic sensors to detect dangerous leaks of carbon monoxide and other toxic gases while trapped deep underwater. Because mice have much faster metabolisms than humans, they would conveniently drop dead or pass out long before the air became fatal for the sweaty sailors sharing the metal tube. This meant the absolute most critical safety system on a multi-million-dollar weapon of war was a small rodent in a tiny cage having a terrible day. Eventually, the military replaced these brave squeaking martyrs with electronic gas detectors, probably because the mice unionized or the crew got tired of cleaning out the cages. It is a sobering reminder that naval superiority once depended entirely on watching a pet store animal to see if it suddenly took an unexpected and highly permanent nap