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The Last Seven Miles

The Bathyscaph Trieste Story

DIVER contributor Don Walsh is the deepest man alive, co-piloting the bathyscaph Trieste to the deepest point in the world ocean – the Challenger Deep in the western Pacific’s Mariana Trench on January 23, 1960. No human has returned to this abyssal region since then and sadly his colleague on that dive, Swiss marine explorer Jacques Piccard, recently died. On the 50th anniversary of this historic achievement, Don tells his story for DIVER readers.

Text by Don Walsh

A Man, a Machine and a Dream

In the late 1930s Swiss physicist Professor Auguste Piccard began development of an ‘underwater free balloon’ for deep ocean exploration.  He’d thought about the concept for many years – since his first year at Zurich Polytechnical School – calling the vessel a‘bathyscaph’,from the Greek words for deep and ship.

The operating principle was simple.  The ‘balloon’ (called the float) was a thin metal shell filled with lighter-than-water gasoline.  Suspended beneath was the thick-walled cabin for the crew.  The float had ballast tanks to provide positive buoyancy while on the surface.  When vented, they filled with seawater allowing the slightly heavy bathyscaph tosubmerge.

Releasing solid weights would slow or stop the descent. For this purpose, ballast containers (shot tubs) were fitted to the float, holding several tons of small steel pellets, or ‘shot’.  Dumping this ballast was controlled by an electromagnet that allowed the shot to flow freewhen it was turned off. In an emergency theshot tubsthemselves could be dropped.

Piccard’s first bathyscaph, FNRS-2, was tested in 1948.  It made a manned test to 90 feet (27m) and a single unmanned dive to 4,600 feet (1,400m). Both were successful but the submersible proved unseaworthy on the surface; it was taken to the French naval shipyard in Toulon for a complete reconstruction and upgrading.  In June 1953 the French Navy launched their first bathyscaph, the FNRS-3,which used many of its predecessor’s parts.

After working briefly with the French, Professor Piccard and his son Jacques went to Italy and organized a consortium of Swiss and Italian sponsors to build a new bathyscaph, Trieste.  Launched on 1 August 1953, it represented lessons learned from FNRS-2 and their work with FNRS-3.  By the end of September,father and son had made a dive to 10,392 feet (3,200m) in the Tyrrhenian Sea, near the Island of Ponza.

Trieste Joins the Navy

The Piccards soon found Trieste’s operational costs were too much for them to manage.  In 1954 she made one dive; in 1955 it did not operate at all.  By 1956 they were looking for an organization to lease it on a long-term basis.  Among others, the British and American navies were approached.  Only the U.S. Navy’s Office of Naval Research (ONR) in London showed any interest.

In 1957 ONR contracted for a series of demonstration dives at Capri.  From July to October a total of 26 dives involved marine scientists from a wide variety of disciplines.  Each was tasked to evaluate how this platform could improve the way he did his science. At the end of the Capri program, it was recommended that the Navy acquireTrieste.  Purchased from the Piccards in January1958,it was shipped to San Diego that summer.

The Navy Electronics Laboratory (NEL) there would be the new home of Trieste. In addition,ONR hired Jacques Piccard and Giuseppe Buono as consultants tohelp the Navy learn how to operate and maintain the submersible.

Dr. Andreas B. Rechnitzer became the newly mintedchief scientist and manager for the program. He knew a good deal about Trieste, havingparticipated in the 1957 Capri dives and from mid-1958 he’d been busy at NEL putting together the sub’s shoreside infrastructure.

My Strange Journey Begins

In 1958 I was a submarine lieutenant temporarily serving on the staff of Submarine Flotilla One in San Diego.  It was a big command, with 24 submarines and four support ships.  The flotilla Commodore thought that he should have an aide. However, his personnel allowance did not provide for one, so it was decided to recruit an officer from one of the submarines for this unofficial appointment.  I had the ‘honor’ of being the first to be ‘shanghaied’.

I had to figure out how to get back to sea and NEL’s Dr. Rechnitzer proved to be my salvation.  One warm summer’s day he came to my office aboard the submarine tender to ask if he could give aTrieste briefing for the Commodore.  I asked the boss and he said, “Yes, invite him to lunch and you should come too”.

Andy brought Jacques Piccard with him.  Over lunch they briefed the Commodore on plans for the bathyscaph, how it worked, future importance to the Navy, etc.  The Commodore thanked Andy and asked how the Submarine Force could help.  Without hesitation, he said, “We need two submarine-qualified officers and about five enlisted men to maintain and operate Trieste, and we need them soon.”  He stressed that while NEL would provide logistic support and scientific program guidance, a military crew was needed to operate and maintain the vehicle.

It so happened that Trieste had arrived aboard a cargo ship and on the day of our luncheon, Andy arranged for the barge carrying the disassembledsubmersibleto be brought alongside the tender. Looking over the side, I thought the collection of odd bits of metalmore likely resembledthe aftermath of a boiler factory explosion.  I thought to myself that I’d never get into that thing…

The Commodore thought Andy’s personnel request was reasonable and said he would take care of it. I was directed to send a message asking for two officer volunteers.  Out went the messageto all subs operating on the west coast. The response was curious; just one name came back. It struck me that this situation could be my return ticket to sea duty – a special kind of duty admittedly – but at least I’d be at sea. So I offered to fill the ‘quota’ and subsequently received orders to report to NEL.  The Commodore kept his promise and I got out from behind that desk…

A Fast Education In Bathyscaphing

The first officer volunteer arrived at NEL in December 1958. He was a couple of years senior to me and was appointed Officer-in-Charge of Trieste.He was present when the newly assembled Trieste made its first U.S. Navy dive, an historic moment somewhat lost by the fact that neither he nor Andy were on board with Jacques.  It was a freelance photographer on assignment for NBC who accompanied Piccard.

I got to the laboratory in January1959 and became the Assistant Officer-in-Charge.  Before long, however, my colleague fell ill with a condition demandinglight duty and a fairly prolonged period of recuperation.  Sadly, he had to leave the program. Thereafter, I became the O-in-C and soon found an assistant in Lieutenant Larry Shumaker,who’d served with me aboard the submarineRasher. I knew he had the energy and intelligence for the job and we got along very well.Before long he was ordered to NEL as the Assistant Officer in Charge.

The first months of 1959 were very busy making dives off San Diego in Trieste’s ‘as delivered’ configurationbutbefore she was sent to the naval ship repair facility for conversion work I did manage a dive to more than 4,000 feet (1,200m) in the San Diego Trough.  I was very impressed. And I realized that this kind of seagoing was exciting!

It wasn’t until I was on the job that I learned what only afew ‘insiders’had in mind for the bathyscaph. The plan, it turned out, was to dive Trieste to the deepest known place in the World Ocean – the Challenger Deep in the Mariana Trench, which is about 200 miles (320km) from the Naval Station at Apra Harbor, Guam, in the western Pacific.  Depth: seven miles give or take!Andy’s briefing to the Commodore had neatly sidestepped this detail.

This was pretty exciting stuff for a couple of submariners whose knowledge of ocean depths was generally limited tothe test depth of the boats they served on and the coastal bathymetry where they might be operating.  The last sub Larry and Iserved on operated to maximum depth of 300 feet (91m). This contrasted dramatically with the bathyscaph whose depth rating and dive capability added up to so many thousands of feet that it was easier to measure the depth in miles…nearly seven of them.

To accomplish this deepest of divesTrieste would need significant modifications. As delivered it could reach a maximum depth of 20,000 feet (6,000m), a limit imposed by the strength of the personnel sphere/cabin and the amount of gasoline or buoyancy that the float could carry.  It was apparent that both a new cabin and enlarged float would be needed.

The new sphere was ordered from the Krupp Works in Essen, West Germany.  It would be built to withstand 50,000-foot(15,300m) maximum depth pressure – if any place in the ocean were found to be that deep. The Krupp sphere was a thing of beauty.  Five to seven inches thick it was made in three rings and glued together with epoxy at the two joints.  When the Admiral heading the Navy’s Bureau of Ships came to see Trieste at NEL, he asked how this very smooth sphere was fastened together and so I told him, “It’s glued.” He fixed me with an Admiral’s ‘evil eye’ stare and said, “Lieutenant Walsh, the Navy does not glue its ships together!”  Perhaps, but ours was…

Based on our design specifications the naval ship repair facility in San Diego upgraded the float.  Basically it was lengthened to increase our gasoline capacity from 28,000 to 34,000 gallons (106,000-130,000 litres). In addition bigger ballast tubs were built to increase shot capacity from 11 to 16 tons.

As the yard work progressed we developed an operational plan for our deep dive program, now named ‘Project Nekton’.  While ONR had provided the funds for upgrading the Trieste, the policy arm of the Navy had not yet been informed of the deep dive program.NEL’s Commanding Officer approved our plan, which was sent forward to Washington, DC. But with so much at stake, and no time to waste, it was agreed that I go back east, too, to push it along.

Once there I was put on sort of a ‘conveyor belt’.  The commanders passed me to the captains who in turn passed me to the admirals.  And even within the ranks of the flag officers I still moved upward rather rapidly without any real decisions being rendered.  After not too much delay, I found myself in front of Admiral Arleigh Burke, the Chief of Naval Operations.  I knew I was going to get an answer from this man and – reluctantly – he authorized the project following my briefing, but with the caveat of no publicity until we were successful. He did not want a high-visibility flop. I called NEL and gave them the good news.


The modified Trieste was reassembled and did two test dives off San Diego in mid-September to ensure proper function of all the modifications.  Then we took it apart and loaded it on a commercial cargo ship bound for Apra Harbor at Guam.  The ship sailed October 5 with two enlisted men along for security.

The rest of the team of three military and seven civilians from NEL flew in to prepare our support base.  The situation at Guam was excellent.  We had outstanding support from the Naval Repair Facility and Naval Station. From top to bottom, the Navy on Guam wanted to help us.

Working from dawn to dusk, seven days a week, our little 14-manteam of military and civilian personnel began a series of increasingly deep test dives from November to December 1959.  All seemed to be working well.

Then on November 15, Andy and Jacques set a new world depth at 18,150 feet (5,500m).  The previous record of 12,300 feet (3,750m) had been set in 1954 by the French Navy’s FNRS-2 bathyscaph.

In The Glue

However, a significant problem was encountered. During the six hour dive the sphere was ‘soaked’ in very cold seawater, long enough for the metal to become quite cold.  When the bathyscaph surfaced into the warm tropical waters, the differential expansion across the joints caused the glue joint to fail with a great bang.  This was not inherently hazardous; sea pressure would hold the sphere’s three pieces in place.  But it was clear that we’d have to drydock Triesteand the big worry was if the sphere’s three pieces would slide apart without the benefit of sea pressure holding them together.

Very gently the bathyscaph was set down on its cradle.  The three components of the sphere did slip a bit but only few thousandths of an inch.  And there was evidence of some saltwater weeping inside the cabin. Taking the sphere apart on Guam was out of the question.  So we could not clean and re-glue the joint.  Our very creative machinist Chief Petty Officer John Michel took charge of the fix.  He realigned the three pieces almost perfectly using a forklift truck and a large timber ‘battering ram’ to jolt the pieces into approximate alignment.  Then he built a series of bands that went around the outside of the sphere to mechanically hold all the pieces together in alignment.  Rubber bands covered the sphere joints and an automotive gasket compound was used to make them watertight. It was a remarkable piece of ‘shade tree engineering’ that saved Project Nekton.

It was difficult not telling our masters in San Diego about this minor operational problem.  But we felt that any whiff of the problem would result in an order to cancel the program.  We managed to maintain ‘security’ pretty well, even with several of our temporary civilian workers moving back and forth between Guam and San Diego.  You could hardly blame a person for ‘spilling the beans’. It was a hell of story…

A month later, the repaired Trieste was back in the water.  On December 14we made a test dive in Apra Harbor and a few days later 50 miles (80km) offshore Jacques and I dove to 5,450 feet (1,660m), completing operations for 1959,a year during which Trieste made 13 dives with the U.S. Navy.

During the Christmas holiday season Andy, Larry and I made several pilot training dives in the harbor sincesubmersible readiness procedures, piloting skillsand post-dive requirements were independent of dive depth. The difference between shallow and deep diving was mostly the dive duration.

January 1960

On January 15Jacques and I dove to 23,000 feet (7,000m) in the Nero Deep.  We didn’t land after sighting the seabed. Time was tight and we needed to get back to Guam as soon as possible to readyTrieste for her deepest dive. Also, the dive was cut short because the submersible had sustained some external damage during the tow.

On the January 19 our little flotilla departed Apra Harbor for the Challenger Deep.  The towing vessel was USS Wandank (ATA-204) and USS Lewis (DE-540) was our ‘headquarters ship’. It would be a long 200-mile (320km) tow for Wandank, steaming at a steady as she goes five-knotspeed.  Jacques, Larry and Buono were aboard to monitor the tow because even at that slow speed we were very concerned about possible damage while at sea.

Andy and I were on board Lewis, which went ahead to the dive site vicinity where we needed to make anacoustic survey to locate the Challenger Deep.  Lewis’ depth sounder could not ‘see’ the seafloor at such a great depth so Andy developed a scheme to use small blocks of TNT.  We’d start a stopwatchwhen the charge exploded and stop it when we heard the return echo on the ship’s fathometer hydrophone. We didn’t care about exact depth measurement, only that 14 seconds was deeper than 12 seconds, and so on.

When Wandank arrived on site January23 we were pretty sure we’d ‘mapped’ a zone about four miles long and one mile wide (6.4 by 1.6km). While the day was clear, the sea state was 7 to 8, worse than on the Nero Deep dive.  This made it difficult to ready theTrieste for the dive but it was accomplished and fortunately there was only minor damage from the long tow.

Finally we dropped the tow in the center of the target area and prepared to dive at about eight in the morning.With all preparations completed we closed and bolted the heavy entrance hatch and by half past the hour we were on our way, hopeful of a successful culmination for Project Nekton.

Underwater the ride was a lot better and the descent proceeded smoothly. From 300 to 500 feet (92-152m) we ran into some strong thermoclines and our ‘balloon’ just bounced along on top of them.  We kept valving off gasoline from our maneuvering tank and finally got heavy enough to break through.  This had really slowed us down so we increased our rate of descent. It was important to be back on the surface with sufficient daylight left to prepare Triestefor tow back to Guam. Those were things we did not want to do in the dark in a high sea state.

Between 4,000 and 7,000 feet (1,200-2,100m) a couple of hull penetrators began to weep water drops.  This had happened before and ourremedy was simple: if the number of drops increased with depth, the dive was over and we’d surface, but the drops decreased sothe dive continued.At 31,000 feet(9,500m) Trieste was jolted and a muted bang heard.  On previous dives the failure or implosion of small external components produced sharper sounds but this noise was much lower in pitch, as if something big had broken.

We checked our instrument readings. All seemed well and Trieste was descending at the same rate as before. We decided to proceed. It was evident nothing major had failed.

At about 34,000 feet (10,400m) we turned on our small fathometer, capable of giving us up to a 600-foot trace of the seafloor below.  I monitored it closely while Jacques made the visual check from a single viewport. Our blazing lights reflected off the seafloor, which lightened somewhat the sea beneath us.

At 35,000 feet (almost 10,700m) there was still no indication of the seafloor.  We knew the fathometer was working okaybecause itreflectedthe iron shot we were dropping to slow our descent and by this point we were just barely moving.

Then we passed 36,000 feet (almost 11,000m) and still no bottom in sight. We maintained a very slow descent and, finally, I began to see a bottom trace on the paper chart.  I advised Jacques calling off our distance above the bottom as we closed on it.  Before long he could see the loom of our lights and released just enough shot to make an easy landing.  Our depth gauge read 37,800 feet (11,522m).  We had found a new depth in the Challenger Deep!


We shook hands…expressed a few feelings of joy and relief, too. Everyone on the Project Nekton team had been confident of our successand together we’d achieved exactly what we’d set out to do.  It was a great day for us.Five months of hard work at Guam and all that came before had paid off at the bottom of the sea.

I turned on the aft viewing light and looked through the port in the entrance hatch to find the answer to the ‘big bang’ we’d heard at 31,000 feet (9,500m).  The curved acrylic window at the back of the entrance tube had a big crack across it.  This was not a ‘pressure boundary’ since the tube was always flooded during a dive and afterwardswe’d use compressed air to blow out this water at the surface before exiting from the sphere.  If that window failed while blowing down the tube, we could be trapped inside for several days.

After 20 minutes bottom time we had to leave in order to surface in daylight.  We didn’t get any photographs in the zero visibility created by our landing on the sediment bottom. On previous dives the sediment cloud would drift away after a few minutes but on this occasion it did not. The entire time we were on bottom was like being in a glass of milk.

We lifted off at 1:30 p.m., ascending at a good rate of speed. We no longer had to worry about cautious inching forward as we had when approaching the seafloor; now we just dumped ballast and headed home. A three and a half hour ascent brought us back to the surface with plenty of time to secure Trieste in daylight.

Once there we gently filled the entrance tube with compressed air so as to avoid stressing the cracked window.  It was slow, taking 15 minutes for an operation that usually took much less time. As the water level passed below the viewport in the hatch, we could see that the window was holding.  When the last of the water had blown clear we quickly let ourselves out of the sphere, shutting the heavy hatch behind us. Sea conditions were even worse than before and even though our round trip journeywas approximately14-miles (almost 23 km), we managed to surface just four miles (6km) from the Lewisand they spotted us right away. Wandank began to move towards Trieste from about six miles 10km) away.

Back in Guam the Project Nekton principals, Rechnitzer, Piccard, Shumaker and Ireturned to Washington, via NEL, to enjoy a few days of being the center of attention. The highlight was a meeting with the President in the WhiteHouse where he presented us with awards and we gave him one of the American flags and a signed philatelic envelope that we’d taken on the dive. Admiral Burke was smiling a lot more than when I had last seen him and after many rounds of visits with members of Congress and senior officers in the Navy Department we were ready to go back to work.

Jacques went home to Switzerland, his work with the project completed. After some time at San Diego, Andy, Larry and I returned to Guam for Project Nekton II.

For this project all our dives would be for science.  We intended to return to the Challenger Deep for another dive, but the Navy reduced Trieste’s depth capability to 20,000 feet (6,000m), expressing some reservations about the integrity of the sphere. So the deepest dive during Nekton II was to 20,000 feet (6,000m), piloted by Larry with Andy on board.

By August 1960 our operations at Guam were completed and we shipped the bathyscaph and all our supporting equipment back to NEL where Trieste would undergo wear and tear repair and significant modifications based on ‘lessons learned’ while at Guam.  These activities kept us busy for several months.

Trieste was operational again in late 1961 and we began dives off San Diego in support of NEL research projects and during that year our team members began moving to other assignments.  Andy left for an excellent position with North American Rockwell, replaced by NEL’s Art Nelson. Larry returned to submarine duty, replaced by Lieutenant George Martin.  Finally, in July 1962, I was relieved by Lieutenant Commander Donald Keach.

It had been an amazing three and a half years for me. My wish four years earlier to get away from the desk job had come true in a way I couldn’t have imagined.

The Years After

Before we left NEL, Andy, Larry and I had developed a conceptual design for a new bathyscaph. It was clear to us that the nine-year-old Trieste was getting frail and had limited potential for further upgrades.  The Navy approved our concept and Trieste II was constructed at the Mare Island Naval Shipyard in San Francisco Bay.  It was put into service in the late spring of 1964 so none of us had the opportunity to dive in it.

However, tragedy created one more mission for the original Trieste before it could be retired. In April of 1963 the nuclear submarine Thresher (SSN-563) was lost during a test dive off the New England coast.  Once the wreckage had been located by surface shipsTrieste was mobilized to make forensic dives at the site. Based out of Boston, the submersible made several dives during which some small bits of wreckage were recovered.  When it was returned to NEL in the fall of 1963, the vessel was retired as her team awaited delivery of the new Trieste II.

Later in the 1960s the original Trieste II was replaced with another Trieste II,also built at Mare Island.  It had much greater payload capabilities and increased endurance for longer missions – classified operations – that had been delayed by the Thresher tragedy. But another mishap intervened. When the Scorpion (SSN 589) was lost off the Azores in some 9,800 feet (3,000m) of water, the new Trieste II successfully made several dives at the wreck site to help determine what caused this sub to sink.

It was not until the early 1970s that classified work could begin but by this time there were more effective ways to accomplish them.  Finally in 1984, Trieste II was retired at San Diego.  The U.S. Navy had operated bathyscaphs successfully for 26 years. About 250 USN submariners served in these underwater ‘spaceships’ and are entitled to wear the special deep submergence operator pin in addition to their dolphins.

Today one can see the original Triesteat the Navy Memorial Museum in Washington DC and the last Trieste II at the Naval Undersea Museum in Keyport Washington.


For more than a third of a century the American and French bathyscaphs were the only means to get man into the deepest reaches of the oceans. Since the early 1960s over 200 manned submersibles were developed worldwide.  While few remain in service today, we can see our ‘technological fingerprints’ all over most of those developed since ‘our time’.

The ability to perform deep underwater operations with manned and unmanned vehicles now exists in many places around the world.  There are four manned submersibles – two Russian, one French and one Japanese – that can go to 20,000 feet (6,000m). As well, there’s a new one currently in sea trials in the Peoples Republic of China.  It can dive to 23,000 feet (7,000m) and will be the deepest diving manned vehicle in the world.

By contrast, the U.S. Navy no longer has manned deep-sea vehicle capability. The U.S.- based Woods Hole Oceanographic Institution does have a program to replace its venerable Alvin with a new submersible that will be able to dive to 21,320 feet (6,500m). Partially funded, that program is moving very slowly.

Will anyone ever go back to the Challenger Deep? It’s hard to say, although there was one serious project underway by adventurer Steve Fossett who was having a one-person submersible built at the time he died in an airplane crash.  His vehicle was about two months away from completion at that time.  Also, there have been rumors that Sir Richard Branson and film mogul James Cameron might be interested in diving into the Challenger Deep.

In 1995, the Japanese unmanned Kaiko remotely operated vehicle (ROV) made a dive to this site.  And a couple of years later they went back again.  Then in May 2009, the Nereus unmanned submersible dove and spent some time at depth.  Perhaps with the increasing capabilities of unmanned vehicles there will no longer be the need to send man to this extreme depth.  Personally, I think that would be a real loss for the spirit of manned exploration.  We must continue to go there…

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One Response to “The Last Seven Miles”

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