The Johns Hopkins University Applied Physics Laboratory is a not-for-profit university-affiliated research center (UARC) in Howard County, Maryland. It is affiliated with Johns Hopkins University and employs 8,700 people as of 2024. APL is the nation's largest UARC.

A proximity fuze is a fuze that detonates an explosive device automatically when it approaches within a certain distance of its target. Proximity fuzes are designed for elusive military targets such as airplanes and missiles, as well as ships at sea and ground forces. This sophisticated trigger mechanism may increase lethality by 5 to 10 times compared to the common contact fuze or timed fuze.