The submarine USS Dolphin was specially built as a test-bed for deep-diving designs.
"Museum Pieces" is a diary series that explores the history behind some of the most interesting museum exhibits and historical places.
USS Dolphin on exhibit at the San Diego Maritime Museum
At the outbreak of the Second World War, a typical submarine or u-boat was capable of diving to a maximum depth of round 250 feet. By the time the war ended, advanced models like the American Tench class could reach depths of 450 feet. Any deeper, and the increasing water pressure would be too much for the hull to withstand, and the submarine would implode.
For the most part, however, WW2-era submarines were surface ships, cruising under diesel power and submerging only when they were stalking an enemy ship or evading enemy destroyers or aircraft.
By the 1950s, though, this had changed. The advent of nuclear power meant that submarines could now stay submerged for very long periods, and the development of new sonar systems meant that they could be detected even at depth. The Navy needed a new type of sub that could submerge and operate at much greater depths. This became even more important as plans were made for subs that were armed with Polaris nuclear missiles. These were intended to lurk in the depths indefinitely, ready to surface and launch their missiles at a moment’s notice.
So in 1960 the Navy issued orders for “Project SCB 207”, a purpose-built submarine that would be christened AGSS-555 Dolphin. Construction began in November 1962 at a shipyard in Maine, and the finished sub entered service in August 1968.
Because the Dolphin was intended solely as a test and research platform, she was very small for a submarine—only 152 feet long and displacing less than 1,000 tons. She had no torpedo tubes or deck guns, and she was driven by a pair of General Electric V-71 12-cylinder diesel engines, making her the last non-nuclear-powered submarine to be launched by the US. The Dolphin’s tiny engine room was so small that standard US Navy engines could not fit, so they installed modified diesel engines that were used for city buses.
Dolphin was specifically designed to reach the maximum possible depths that could be reached with current technology. Unlike the tapered “fish” shape used in WW2 subs, she was designed with a tube-shaped inner pressure hull with a constant diameter and a hemispherical cap at both ends, allowing her to better withstand the water pressure at depth. Only the external tail, which was outside of the internal pressure hull, was tapered.
To make the hull as strong as possible, there was only one hatch, and the “snorkel” which allowed air to reach the diesel engines while submerged was dropped: Dolphin had to surface and open her hatch whenever she was running on diesel. While at depth, she was powered by her bank of silver-zinc batteries, which powered two electric motors that did not require air to operate. Her complement of around 30 men could stay underwater for up to 15 days.
The ship was also fitted with a specially-built Submarine Safety Monitoring System (SSMS), a network of sensors which constantly monitored and recorded measurements of temperature and pressure, sounded an alarm if anything reached the danger zone, and was capable of automatically blowing the ballast tanks and surfacing the sub if necessary. Inside, the sub could carry up to 12 tons of testing equipment, and she had external hardpoints where additional equipment could be carried.
Three rotating crews were assigned to the sub, each specially-trained and qualified at levels higher than other service subs.
Within a few months of her commissioning in 1968, the sub began a series of test dives. On one of these missions in November she set a depth record which is still classified but which was at least 3,000 feet, a record which still stands. (Officially, the Los Angeles class nuclear submarines can reach 850 feet, but unofficial sources have cited figures over 1,000 feet, and it is assumed by most experts that it can reach much deeper.) In August 1969, Dolphin carried out another experiment with a torpedo launched from an external tube mounted to the hull called DEXTOR (for Deep External Torpedo)—another record which still stands.
For the next four decades, Dolphin carried out research and testing missions, and helped the Navy develop better submarine-to-aircraft communications using extremely-low-frequency (ELF) radio antennae and later lasers, and new non-acoustic anti-submarine warfare methods. She also carried out underwater mapping and photographic missions, deep-water surveys, and evaluation testing of new equipment including sonars and towed detection devices. Many of her missions remain classified. Lessons learned from the Dolphin’s experiments would be incorporated into each new generation of nuclear submarines.
The sub also became a platform for scientific research. When some physicists at CERN hypothesized about a “fifth force of nature” which acted as a repulsor over very short distances, Navy researchers took cubes made from various materials to great depth aboard the Dolphin and carefully measured their gravitational attraction. They were unable to find any evidence for the postulated “fifth force”.
In May 2002, Dolphin was on a routine mission off the coast of California when she developed a leak in the torpedo room which short-circuited some panels and started a fire. The ocean research vessel William McGraw, which happened to be operating in the area, took on the evacuated crew, and the Navy service ship Kellie Chouest towed the crippled sub back to shore, where she underwent a $50 million repair and upgrade before returning to service in 2005.
But by this time, Dolphin was 37 years old, making her the longest-serving American submarine, and she was costing the Navy some $18 million a year to operate. In 2006 it was decided to withdraw her from service. Her final voyage was in September of that year, and she was struck from the Navy register in December.
In 2008, Dolphin was donated to the San Diego Maritime Museum, where she went on public display on July 4, 2009.
Some photos from a visit.
A model showing the cylindrical hull
Inside the sub. It’s awfully cramped in here.
Sonar room
Radio room
Command Bridge
Officer’s quarters
The galley
The upper engine room
NOTE: As some of you already know, all of my diaries here are draft chapters for a number of books I am working on. So I welcome any corrections you may have, whether it's typos or places that are unclear or factual errors. I think of y'all as my pre-publication editors and proofreaders. ;)
