There is a difference and it is one of the things that separate smokeboats from nukes. Ignoring propulsion power except for the fact that one lets a boat stay down forever, diving is an art, submerging is a life style.
On smokeboats, diving is life. Like all submarines, they are safer below the surface. But since they must surface for air to charge batteries, they must always be ready to dive. They always say 'dive' because it's done in a hurry. It's practiced over and over, do it fast. Do it safe, but you damn sight better get down in a hurry. Over and over always striving to get to periscope depth in under a minute. In World War II, 50 seconds or less was strived for religiously. That Jap plane would be out of the sun and on your ass with a 500-pound bomb that would ruin your whole day. The 'tincan' with a bone in its teeth would be out of a fog bank and blasting away with a 5-inch gun in a few seconds. You had better be able to pull the wave tops over your head in a hurry. Then you had to go deep fast so his string of ashcans wouldnt go off at a deadly hull-cracking range. The deeper and the quicker you went down, the better for your chances of survival .
Us Cold War sailors were trained by combat veterans and if you wanted their respect, you went down fast. For safety's sake, we didnt try to shave those last 5 seconds off, but they would blister your hip pockets if you hung around on the surface. Once you were past your trim dive, it was time to get serious. The command "Dive, Dive" meant something like, "Get me down, NOW!"
So we practiced and practiced, until it was ingrained, the alarm sounded and down we went as quick as possible. Guys not on watch did things to speed up and make safer the process. It was not unusual to see an electrician passing through the engine room stop to spin a valve shut or trip the engine air induction valve. Then walk on forward without a word, it was just done, no one thought about it. In other parts of the boat things were done, reports made, guys helping out because they were nearby. It was making an art of combining speed and safety.
It was our art and we loved it, for it was what we were all about. Diving - the act - was an end unto itself. Submerging to a nuclear powered boat was just a beginning of a cruise. Smokeboats made more dives in a year that nuke boats do in a lifetime now.
Nuclear power changed all that and for the better I'm sure. But its no longer an art, its a lifestyle. Once down under nuclear power, you stay there. For weeks or months even, once down its for the duration. Submerging is a slow methodical process, with cross checks and safety foremost. They dont even say "Dive" anymore, It's "Submerge the ship." Submerge sounds permanent, dive says this is temporary, we will be back soon.
I watched a tape of a boomer submerging for its patrol, it took about 6 minutes. Hell, a New London school boat could go down and back up two, maybe three times in 6 minutes. Of course the oilers would have mutinied from having to open and close their 32-turn exhaust valves that many times.
Science often surpasses art in practical things and thats okay, its progress. Submarines today do more things better, faster, and safer than we did. The idea that the seven seas could erupt with flying death to rain down upon their heads, kept the Russians from doing anything supremely stupid during the Cold War. Boomers and fast attacks helped to win the Cold War with science that the Soviets couldnt match. Hell, they didnt even know where all those missiles were and spent themselves into oblivion trying to keep up.
But please forgive this old-timer when he remembers with a smile when diving a submarine was as much art as science. When eighty young men not long from high school, welded themselves into a crew that took aging submarines to sea. A crew that could drive a boat under in 55 seconds safely day after day, time after time. It was our life, diving was what we were all about. Diving was what we did, without it the submarine and we were less. It gave us pride and confidence in ourselves. More importantly, it gave us pride and confidence in others and made separate men into a crew. Even today, we think of what we did as one of the golden moments because diving was an art that pleased and satisfied the heart and soul, not a plodding scientific lifestyle.