The ARPA may swap targets when automatically tracking if two targets __________.

The correct answer is that the ARPA (Automatic Radar Plotting Aid) may swap targets when automatically tracking if two targets pass close together. This is because ARPA systems rely on distinguishing between multiple targets in a radar display, and when two targets come very close to one another, the system can struggle to differentiate between them. This may cause the system to mistakenly track one target while confusing it with another, leading to an automated swap of the target being tracked.

When targets are closely spaced, it can create issues with radar return signals where overlapping echoes can cause confusion in the data processing algorithms. This situation highlights the importance of maintaining adequate separation between tracked vessels to ensure accurate navigation and tracking.

In contrast, other scenarios, such as targets being at the same range, on reciprocal bearings, or being tracked on the same bearing, may not necessarily lead to confusion significant enough to cause the ARPA system to swap targets. These conditions do not inherently create ambiguity in target identification as much as physical proximity does, thus making close proximity the key factor for target swapping.