On February 4, 1989, the U.S. Department of Defense publicly acknowledged that a small radioactive source integral to certain tests and equipment had been lost or was unaccounted for. The admission followed internal reviews and inquiries about inventory controls for radioisotopes and raised questions about how such materials were tracked and secured. Background During the late Cold War, the U.S. military and associated laboratories routinely used sealed radioactive sources for a range of purposes including instrument calibration, radiation detection training, and component testing. These sources typically contained small amounts of radioisotopes encapsulated to prevent leakage and exposure; nonetheless, their loss or misplacement posed regulatory, safety, and public-relations challenges. What was disclosed The Pentagon statement indicated that officials had identified at least one sealed source that could not be located. Public and press accounts at the time described the material as small in physical size though radioactive enough to require tracking under federal regulations. Officials emphasized that initial assessments suggested no immediate risk to public health, but acknowledged the loss reflected lapses in recordkeeping and property control procedures. Response and investigation Following the disclosure, the Defense Department and affiliated agencies undertook searches of storage facilities, laboratories, and testing ranges where the source might have been used or stored. Internal reviews examined inventory systems, personnel responsibilities, and chain-of-custody practices meant to prevent such losses. The incident spurred calls from some members of Congress and watchdog groups for tighter controls and improved reporting to the Nuclear Regulatory Commission (NRC) and other oversight bodies. Context and implications Lost or misreported sealed sources have been a recurring concern in civilian and military sectors because, while many are small and pose limited hazard if intact, they can be dangerous if breached or handled improperly. The 1989 Pentagon admission underscored vulnerabilities in property management during a period of extensive experimentation and decentralization of testing activities. It also added to broader public scrutiny of how defense agencies managed hazardous materials. Limitations and records Publicly available accounts from the time provide limited technical detail about the isotope involved, the exact quantity, or the circumstances of its disappearance. Some contemporary reports referenced ‘‘a small source’’ without specifying type; government summaries focused on procedural failures rather than health impacts. As with similar incidents from that era, precise archival records may be restricted or incomplete, and researchers rely on official statements, press reporting, and later policy changes to reconstruct events. Aftermath The disclosure contributed to subsequent efforts to strengthen material accounting, improve labeling and storage standards, and reinforce reporting requirements for dislocated radioactive sources across federal facilities. Agencies revised inventory protocols and increased coordination with civilian regulators. No widely reported public-health incidents were directly linked to this particular loss in 1989. Why it matters The case illustrates how even small, regulated radioactive materials can become matters of public concern when oversight and recordkeeping fail. It also reflects ongoing challenges—then and now—in ensuring secure management of hazardous materials across large, decentralized organizations such as the Department of Defense. Sources and verification This summary is based on contemporaneous press reporting and public statements by defense officials from February 1989 and on later discussions of inventory-control reforms. Where details were not publicly disclosed or remain ambiguous in the record, this account notes those limits rather than speculating about specifics.