The radar control used to reduce sea return at close ranges is known as what?

The correct answer is Sensitivity Time Control (STC). This feature is designed to enhance the clarity of radar images by selectively suppressing or attenuating echoes that originate from nearby sea surfaces or clutter, which can severely hinder the radar's effectiveness. By applying STC, the radar can dynamically adjust its sensitivity based on the distance of the targets; for instance, it reduces the gain for close-range signals while maintaining full sensitivity for more distant echoes. This adjustment helps to differentiate between actual targets and unwanted clutter from the sea surface, enabling mariners to obtain clearer and more accurate radar readings in environments where close-range returns might otherwise overwhelm the display.

The other terms listed do have their functions but are not specifically aimed at reducing sea return at close ranges as effectively as STC. Gain control generally refers to the overall strength of the radar signal and might not specifically target close-range clutter. Fast time constant is related to the radar's response time in filtering out noise but does not directly address sea return issues. Pulse length control alters the duration of the radar pulse, affecting resolution and range but not specifically focusing on mitigating close-range sea returns.