submerge vs submersion

submerge is not a noun while submersion is a noun.

Word	Noun	Adjective	Verb	Adverb
submerge	No	No	Yes	No
submersion	Yes	No	No	No

submerge (noun)	submersion (noun)
	the act of wetting something by submerging it
	sinking until covered completely with water

submerge (verb)	submersion (verb)
fill or cover completely, usually with water
cover completely or make imperceptible
put under water
sink below the surface; go under or as if under water