What brevity term indicates that an object has been acquired and is being tracked with an onboard sensor?

The correct answer is that the term "captured" conveys that an object has been acquired and is being tracked with an onboard sensor. In military terminology, when a sensor has successfully captured an object, it means that it has locked onto and is actively monitoring that target. This is essential for accurate targeting, coordination, and awareness during operations.

The use of "captured" specifically indicates a state of engagement where the onboard sensor can provide continuous updates and information about the object's status and movement. This level of tracking is crucial for ensuring that appropriate tactical responses can be conducted with precision.

The other terms such as "track," "spot," and "contact" have different implications. "Track" generally refers to the process of monitoring an object but does not necessarily indicate that it has been locked onto in the same way as "captured." "Spot" typically suggests that an object has been seen or identified but lacks the connotation of sustained tracking. "Contact" is more about the acknowledgment of the presence of an object rather than the active tracking state indicated by "captured." Thus, "captured" is the most accurate choice for indicating ongoing tracking by a sensor.