The big seal script of character Dive or Diving is
The top in character Dive are two character Owe - 欠 (Post 314).
The top in character Substitute are two character Stand - 立 (Post 70).
Substitute means that two guards exchange duty, one is leaving, another is to substitute him. Dive means that people go under water, they have to stop breath which causes the lack of air - owe air or deficiency of air.
The small seal script of the character is
The left is Water Radical, the right top are two Owe's, even thought they are not in the dictionary, but easy to figure out that they mean Owe (air). The bottom is character 曰 - speak, here means silence.
The clerical script of the character is
The traditional song typeface of the character is
The simplified song typeface of the character is
The problem is what the right part of 潛
means? There is no explanation in any dictionary, but it should be a character in early time, otherwise, people could not have created a compound character 潛.
I guess that the right part of 潛 means that the two people close their mouths, keep silent, just opposite to 替 - open mouths to exchange some words. When people are underwater, they have to keep the mouth closed, and can't speak, which is the meaning of 潛.
The Pinyin of character 潜（潛）is Qian3.