潜る and 隠れる: going beneath a covering and being hidden from view
Compare diving into the sea or burrowing under a blanket with the moon being obscured by clouds, separating movement into a space from visibility.
Going into the water or under a blanket
潜る is read もぐる in this example. 「海に潜って岩陰の魚を観察した。」 says that the speaker dived into the sea and observed fish in the shade of the rocks.
「猫が布団の中に潜って眠った。」 says that the cat burrowed under the blanket and fell asleep. Read both the movement into water and the movement beneath a covering.
The moon obscured by clouds
隠れる (かくれる) means hiding or being concealed. 「雲の後ろに月が隠れると、庭が急に暗くなった。」 says that the garden suddenly darkened when the moon became hidden behind the clouds.
The clouds obscure the moon from view here. Do not add a deliberate action by the moon to hide from someone.
The position entered and what remains visible
The two 潜る examples focus on going into the sea or under the blanket. The moon example with 隠れる focuses on being obscured by clouds and the garden becoming dark.
Going beneath or into something does not always establish disappearance from view. Read 潜る as もぐる here, matching the water and blanket contexts.
Does 潜る always mean becoming invisible from outside?
Show the answer and why
No. These examples concern movement into water or under a blanket. Compare that spatial relationship with the moon being obscured by clouds in the 隠れる example.