Serratia marcescens are Gram-negative bacteria that were often used by the U.S. military and others to track movement of bacteria in the environment. As part of ongoing construction at Fort Detrick, Maryland, what appeared to be a small bomblet was found buried in the ground at the site of an old test grid. A sample of a clear, straw-colored liquid was aseptically removed from the plastic reservoir; the results of routine cultures on standard bacteriological media were negative. DNA was extracted from the sample and found to be 99% identical to S. marcescens. These results demonstrate the ability to identify the contents of a biological munition that had been buried for approximately 50 years.