UNDERWAY ON THE U.S.S. MISSISSIPPI – The Navy's newest fast-attack submarine is speeding down the Florida coast, on its way to its commissioning ceremony in its namesake state, at 15 knots. And it's getting outraced by dolphins.

Hours before the U.S.S. Mississippi dives several hundred feet beneath the Atlantic, its sail juts proudly into the warm, whipping southern air. Submariners allow me to see the highest point on the sub for myself – provided I can keep my balance up three steep levels' worth of ladder and hoist myself out onto a platform the size of a fancy refrigerator. A harness hooked to an iron bolt on the sail keeps me from falling to my death. There's no land in sight, just blue water turned white around the sub's wake, a tall BPS-16 military radar spinning in front of us, and a family of dolphins jumping out of the surf in front of the 377-foot boat.

Apparently it's typical. Where subs travel in the southern Atlantic, dolphins tend to tag along, eager to say hi to their large, silent playmate. "Dolphins like to sing," notes Petty Officer Joshua Bardelon, a 32-year old from Pascagoula, the site of the Mississippi's destination, who supervises the boat's sonar systems.

Those systems are part of why Navy Secretary Ray Mabus is eager to take possession of his newest Virginia-class submarine when it formally joins the fleet on June 2. As much time as it spends listening to dolphin symphonies, the Mississippi is everything from a weapon to destroy other ships to an electronic-attack system to a stealthy transport for Navy commandos.

The multiple sonar arrays allow the submarine to detect other ships before it's detected itself. Underway, the boat is dead silent except for the hum of the air conditioning, an indication of the classified tools that mask the Mississippi's acoustic and electronic signatures to maintain its exceptional stealth. Then comes the boat's electronic warfare capabilities – which its crew will discuss only vaguely.

"If I'm at periscope depth and I stick my periscope out of the water, people who are looking for me will be using a radar system to find me," says the sub's commander, Capt. John McGrath, a 20-year submarine veteran. "But I will know that that radar is in the area and I will use that to my advantage."

Some of its other weapons are more traditional. The torpedo room, down in the deepest level of the boat, hosts 16 intimidating metal tubes, each wider than bicycle wheels, the bays for its 28-foot torpedoes and Tomahawk missiles. The room looks like a machinist's workshop, except for the exercise bikes and the racks where the torpedomen sleep beside their weapons – the primary means for the Mississippi to complete its future missions: hunting and destroying enemy ships and subs.

"There are two types of ships in the Navy," explains Chief Nathan Holmes. "We have submarines, and we have targets."

Even though the Mississippi isn't on a combat mission – which is why the Navy allows me to tag along on a boat overflowing with classified systems – McGrath is eager to demonstrate that his boat is a predator, not prey. After I climb down from the sail, he orders the boat's pilot to dive to 155 feet, a way-station depth that's far enough underwater to avoid sea traffic but shallow enough so he can get surface rapidly should something go wrong. When nothing does, McGrath orders the pilots to continue on to a depth of 400 feet. The faster the captain wants to go, the deeper he dives.

The dive is surprisingly imperceptible. Even though we've just dropped 400 feet in a minute, I barely lean forward. If I had been drinking anything, it wouldn't have spilled.

That's the case during my entire four-day stint on the boat. With the exception of a 20-minute exercise in dipping the Mississippi up and down – a queasy affair nicknamed "Angles and Dangles" – I've had rockier trips aboard surface ships. The fast-attack submarine is downright placid, even at 20 knots.

The steadiness will be an asset for one of the Mississippi's other missions: aiding Navy SEALs. There's a special bay, called a lockout trunk, that allows a tinier sub to dock and deposit a small number of SEALs onboard. Once they're aboard, the Mississippi will become a Navy special warfare platform – as are many subs that don't carry nuclear missiles – performing reconnaissance missions and getting SEALs stealthily in and out of where they need to go. The Virginia class' smaller size allows the sub to "be more maneuverable in a littoral," says Master Chief Bill Stoiber, the chief of the boat, or senior enlisted man aboard, making it particularly useful for SEAL insertion missions. After the summer, the Mississippi will head for southern Florida to test its special-warfare skills.

As much as the Mississippi is the newest in new for Navy subs, not everything aboard is super-advanced. Satellite connectivity is limited. Submariners like to stay autonomous when they're below the waves, but that means that information aboard the sub largely stays on the sub, and outside information doesn't always reach the boat quickly. The Mississippi rises to periscope depth – that is, shallower than 60 feet below, so its periscope can stick its neck out of the water – in order to fire off e-mails or receive communications through classified and unclassified-but-secured networks. Even so, submariners roll their eyes at how slow their connection speeds are. (Think dial-up. In the late '90s.)

When the sub needs it, it can request extra satellite bandwidth from the Navy – often to send off a video or larger data file. But that "spot beam" is only for special occasions, and it's a one-off event. Persistent, available undersea bandwidth is a challenge the Navy hasn't yet figured out how to solve.

Then there are the traditional joys of life aboard a submarine. The Mississippi is home to 138 men, who have to get very comfortable with each other, since there's nowhere to go for privacy. The halls are barely wide enough for two people hugging the walls to traverse. Submariners are billeted up to 47 per room, stacked up in threes on narrow racks. A typical deployment entails six months of living in these cramped conditions, and the Mississippi is capable of staying underwater for 90 days at a stretch.

Still, the ship makes a virtue out of solitude. The food is unexpectedly excellent. It's difficult to store bread underneath the sea without it molding or going stale – and there's no place to buy more – so the kitchen bakes it fresh every day. It's tempting to forego a lunchtime hot dog just to eat a delicious empty roll an hour old.

The most striking demonstration of the crew's tightness comes in the control room. Unlike older subs, the Virginia class doesn't hive away its sonar stations. The dark room, illuminated by dozens of screens displaying torrents of highly classified data, joins up the pilots, navigators, weapons experts and sonar technicians. Five sonar techs stare at screens filled with green representations of the sounds of the ocean while they listen through headphones. Should they hear an enemy ship they're hunting, they can holler at the fire control station on the other side of the control room that it's time to attack.

For now, one of those techs passes me his cans. When I put them on, all I hear is a high-pitched squeak that sounds a little like a squeal of glee. Dolphins.

Photos: Mark Riffee/Wired.com