Which target is generally the hardest to detect on radar at a given range?

Explanation

Echo strength depends on size, height, shape, aspect, and material. Small low craft of poorly reflecting material (fiberglass, wood) return weak echoes and may be lost in clutter or undetected until close. Large metallic, vertical-faced objects (ships, cliffs, bridges) return strongly. This is why Rule 6 warns small craft may not be detected at adequate range, and why radar reflectors are fitted to small boats.

Authority: Bowditch (Pub. No. 9), Radar Detection