Dumb Question

The "Conn" is the shiphandling term for control of the ship's movement, direction, etc. Having the Conn allows one to give direct orders for changes in course or speed.

This is contrasted with having the "deck", which means having responsibility for the ship/ sub as a whole. The Officer of the Deck on a submarine typically has the Deck and the Conn.

On a side note, the Admiral taking the Conn would be a blatant insult to the submarine's commander. It implies a severe lack of trust and is a very serious breach of professional courtesy. This would usually only occur if the captain was being relieved of command for gross incompetence.

"You feel the way the boat moves? The sunlight on your skin? That’s real. Life is wonderful."

When Bruce Dern stated that the Admiral has the con, that meant that the Admiral assumed the duties as the conning officer. On board ships and submarines out at sea, the conning officer is the only person who is authorized to order speed and course changes. Course changes are directed towards the helmsman and speed changes are directed to the crew on duty in the engineering control area of the ship. The bridge of a Naval ship is where the on duty crew controls the ship while out at sea. Because there is often more than one officer present on the bridge, and because the captain of the ship can appear anytime on the bridge, confusion can result if more than one of those officers issues a course or speed change. To prevent this potential for confusion, the helmsman and engineering duty crew are instructed to only follow the commands of the conning officer. So although the captain of the ship can issue speed and course change orders anytime, he/she must state loudly so that everyone nearby can hear that the captain is now assuming the con before issuing any orders to the helmsman and engineering duty crew.

p.s. I have served as a conning officer aboard Naval ships on many occasions.