USS Dolphin (AGSS-555) - The U.S. Navy's Last Diesel Electric Sub

It's the end of an era. The USS Dolphin (AGSS-555) is the last diesel-electric submarine in the U.S. Navy fleet, and it has completed its final underway, during which it made the 1,560th and final dive to a depth of more than 3,000 feet below the surface. Before it was decommissioned, Diesel Power was honored with an invitation to tour the record-setting submarine-and when the Navy asks if you want to go aboard a submarine, there is only one right answer: Yes!

Setting Records
On August 17, 1968, the USS Dolphin (AGSS 555) was commissioned, and it began making history not long after it hit the water. Since the "pressure hull" is a constant-diameter cylinder capped with hemispherical heads (yep, it's a Hemi), it's able to withstand pressures that would crush other submarines. That's why the boat was able to dive deeper than any other submarine and set the still-standing record just months after it was launched. Less than a year later, it was fitted with external torpedo tubes and set another record when it fired one from the deepest depth ever.

Research Milestones
In addition to diving more than a half-mile below the surface of the ocean, the USS Dolphin has spent the last 37 years as a test bed for scientific experiments and technological developments. It was built to be modified inside and out so various types of equipment could be installed for evaluation at sea. The testing led to the development of things such as non-acoustic anti-submarine warfare, submarine-to-aircraft communications, and even a deep-water study of the possible "Fifth Force of Nature." See the sidebar for a list with even more of the Dolphin's accomplishments.

24 Cylinders of Diesel Power
While those achievements are incredible, we bet you are just as interested in the dual 12-cylinder diesel engines that provide power for the submarine. The two-stroke General Motors/Detroit Diesel V71-series engines are each fitted with two superchargers (one for each six cylinders) to pump the output to 425 hp for each engine. These diesels provide the twist to charge the giant 126-cell batteries used to power dual 825hp electric propulsion motors.

As an unexpected bonus during our tour of the boat, the crew (they call themselves "bubbleheads") decided to run the engines for the very last time to clear out the fuel left in the tanks and the fuel lines. The sailors made bets (for bubblehead pride, not money) about how long the engines would run until they starved for fuel. Both engines were started and brought up to about 1,600 rpm, and then we all waited. The number two engine was the first to stop, and about a half-hour later, the number one engine began to surge-and-bog when the fuel delivery became erratic. To find out what happened next, you can watch video clips on our Web site: www.dieselpowermag.com.