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Bathyscaphe Trieste

One intriguing statement regularly repeated is that we know more about outer space than our oceans. And while the accuracy of that fact can be debated, it does highlight how absurdly little we know about the water that covers 71% of our planet.

It’s estimated that as much as 95% of the world’s oceans remain unexplored. Yes, we have mapped the entire ocean floor, but only to a resolution of 5km (3 miles) meaning anything smaller than 5km becomes more or less invisible. The deepest part of our oceans is a section of the Mariana Trench known as the Challenger Deep, located near the Pacific island of Guam. Here, the ocean floor plummets to a depth of 11,034 metres (35, 814 ft) – which is equal to almost 25 Empire State Buildings.  

Reaching it would be the oceanic equivalent of summiting Mt Everest and in January 1960, two men and a Bathyscaphe named Trieste set out to do just that.


Let’s begin with that word Bathyscaphe. A bathyscaphe is a self-propelled, deep-sea submersible – think submarine, but on a much smaller, more rudimentary scale, that can go even deeper. For all of the linguists out there, the word bathyscaphe is composed of two Ancient Greek words; bathys, meaning deep and skaphos, meaning vessel or ship. 

The bathyscaphe was invented by Auguste Picard, a physicist, inventor and all-round old fashioned explorer the likes of which we just don’t get anymore. Much of his early work focused on helium balloons and he became one of the two first people ever to reach the Earth’s stratosphere in 1931. After 27 balloon flights, his final height record (and world record) stood at 23,000 metres (75,459 ft) – which incidentally, is an astonishing 27 Burj Khalifas stacked on top of each other. 

But Picard wasn’t just focused on the sky. Later, he turned his attention to our vast oceans and set about designing an object that would eventually carry his son to unimaginable depths. 

Picard began building his first Bathyscaphe in Belgium in 1937 but work was soon halted due to the outbreak of World War II. It wasn’t until 1948 that FNRS-2 finally appeared (FNRS-1 had been one of Picard’s final balloons).

After achieving a then world-record 4,000 metres (13,000 ft) it was badly damaged on its way back to port and was eventually sold to the French Navy as funds could not be found to fix it. Parts of FNRS-2 were used for the expanded FNRS-3, which in 1953 broke the depth record again by reaching 4,050 metres (13,290 ft) in the Atlantic, off the coast of Senegal. 

But it wouldn’t be long until that record was obliterated with the emergence of Picard’s Trieste bathyscaphe. 


The Trieste takes its name from the Italian city in which it was built. Picard arrived in Trieste in 1953 to oversee the construction of his design which incorporated scientific and navigational equipment sourced from Germany, Switzerland and Italy. 

The design was similar to previous bathyscaphes but considerably bigger. It consisted of a large central chamber, known as the float, filled with petrol which is significantly more buoyant than water and also much more resistant to compression. The presence of large amounts of petrol (120,000 litres – 32,000 US gal to be exact) meant that this chamber could be built using much more light-weight material when compared to the observation pod at the bottom where the crew would reside and which would need to endure incredible pressure as the bathyscaphe descended. The bottom of the ocean can experience pressure of 1,130 kilograms per square centimetre (16,000 pounds per square inch) – enough to crush a submarine-like a tin can.  

While on the surface of the water, the Trieste’s petrol tanks meant that it remained afloat and only began to submerge when the ballast tanks on either end began to fill with water. To assist with the descent, the small craft also came with two additional ballast tanks called hoppers filled with iron pellets, weighing a total of 9 tons. When the Trieste wanted to surface, the hoppers were discarded with the help of magnets on the top of the craft. This meant that even in the case of power failure, the Trieste could still surface. 

The crew’s cabin, sometimes referred to as the Sphere, was purposely “over-built” with the pressure demands in mind. The walls measured 9 centimetres (3.5 inches) in thickness, while the space itself measured just 2.16 m (7.09 ft) in diameter. The Sphere came with a single, small, tapered glass window using acrylic glass as it was the only known clear material to be able to withstand such pressure. A central entrance tunnel led down from the roof of the bathyscaphe to the observation cabin at the bottom.

Its propulsion came from battery-driven electric motors giving out a rather sedate 60kwh, which gave the bathyscaphe a mighty 2 horsepower. Oxygen was supplied to the Sphere through compressed air, with a long snorkel also attached to be used when the Trieste was still on the surface.

Early Career

The Trieste spent its formative years off the sunny coast of the Mediterranean Sea. Its first dives occurred in 1953 close to Capri in Italy and over the year, a total of seven dives took place, reaching a maximum depth of 3,150 metres (10,334 feet). 

Things picked up in 1956 and 1957 with as many as 36 dives, but the maximum dive limit remained roughly the same. While they were still some way off from the depths of Challenger Deep, the scientific community, and the world, had begun to pay close attention. And it was around this time that Uncle Sam came calling.  

Project Nekton

In 1958 the U.S Navy made an offer of $250,000 (roughly $2.5 million today) for the Trieste which was accepted. The bathyscaphe was transported to the Naval Electronics Laboratory’s facility in San Diego, California, where it underwent a series of extensive modifications with the goal of a truly record-breaking attempt in mind. These modifications included a larger gasoline float, larger ballast tubs, and a newly designed heavy pressure sphere, which was built by a company called Krupp in Germany, producing some of the best quality steel around, not to mention a sizable bulk of Hitler’s artillery, tanks and naval guns. 

The new sphere was constructed of three delicately machined sections: an equatorial ring and two hemispherical caps and now weighed 13 tonnes while out of the water and 8 tons in it, while the walls now measured 12.7 centimetres (5.0 in) in thickness. 

The American operation came to be known as Project Nekton, which, apart from the main objective of reaching Challenger Deep, came with several scientific goals, including;

  • Water current measurements
  • Determining sound velocity at low depths
  • Studying organisms 
  • Geological studies of the trench
  • Studying hull effects at significant depths.

But let’s also not forget that this was the late 1950s and competition between the USA and USSR was hotting up, so no doubt the added glory of reaching the lowest point of our oceans but also have played some kind of factor. 

But this needed to be a slow build-up to the main event. The Trieste left San Diego on 5th October 1959 onboard the freighter SS Santa Mariana destined for Guam. Presumably, this ship was chosen for its name, otherwise, it would be quite a coincidence that the ship that set out to explore the Mariana Trench shared the same name. 

The first two dives took place within Guam’s Apra Harbour, while the third reached a depth of 1,500 m (4,900 feet) off the western coast of the island. Though these dives were all well above what would eventually be needed, it did allow the crew to test the Trieste over the same kind of periods needed to reach Challenger Deep. 

On 15th November 1959, the Trieste set a new world record by reaching 5,530 metres (18,150 feet), however, as it neared the surface of the ocean once again a loud bang startled everybody close by. The epoxy glue seals had burst as a result of the Trieste’s segments expanding as the pressure on it eased. Back on Guam, they found that small amounts of water had leaked between the three sections of the Trieste. These seals were filled once again with epoxy glue with some added mechanical holding ring bands for good measure. 

The seventh dive of the Nekton series broke the record yet again as the Trieste reached 7,300 metres ( 24,000 feet) in the Nero Deep area of the Mariana Trench. No doubt frustratingly for all involved, the Trieste couldn’t quite reach the floor of this particular part of the trench which lay a further 15 metres (48 ft) below. This was due to damage to the gasoline release valve located on the top side of the craft which prevented negative buoyancy adjustment and forced the Trieste up. 

As astonishing as this achievement was, it also revealed the dangers of that kind of depth. Several implosion noises occurred on the Trieste as it neared its final depth, with a light inside the bathyscaphe exploding and a topside pipe stanchion used to support some of the scientific equipment collapsing under pressure. It was later found that this had occurred because no compensating holes had been drilled through it which would have relieved the pressure. 

Challenger Deep

The team arrived at their final dive site on 20th January 1960. USS Lewis, which had accompanied the Trieste, was tasked with pinpointing the exact location of the trench measuring just 6.4 km (4 miles) long and 1.6 km (1 mile) wide. The fathometer onboard was not designed to operate at such depths, so the U.S Navy reverted to good old fashioned explosives. By dropping charges overboard then timing the space between the explosion and its echo, the ship was eventually able to find the Challenger Deep – after 300 explosive charges.

With the final location now found, the crews went about preparing the Trieste for what they hoped would be a truly groundbreaking dive.

On 23rd January, the Trieste positioned itself above the Challenger Deep and began to flood her ballast tanks. In the small Sphere, that day was Lieutenant Don Walsh of the U.S Navy and Jacques Piccard, son of the man who had designed Trieste and who had been acting as a supervisor on the expeditions. 

It’s difficult to imagine that either man had experienced a more nerve-wracking 4 hours and 48 minutes that it took Trieste to reach the lowest oceanic point on Earth. At a steady descent rate of just 0.914 m/s (3.29 km/h – 2.04 mph), the dive was remarkably free of incident until the windowpane cracked as the Trieste passed 9,000 m (30,000 feet). If that didn’t send the heart racing I don’t know what will.

No doubt there must have been a great deal of excitement of having reached the bottom of the Challenger Deep, but the situation the bathyscaphe was in meant that the Trieste and its two crew members remained in considerable danger. They stayed on the ocean floor for just twenty minutes, apparently eating chocolate to keep their energy up as temperatures had dropped to just 7c (45F). 

As they stared out of the small, now cracked, window they saw what appeared to be a small sole and flounder close to the Trieste, however, this claim was later questioned. Theoretically, the lowest possible depth that fish can survive is thought to be around 8,000–8,500 metres (26,200–27,900 ft), lower than that and they would become hyperosmotic, meaning that they would basically begin to shrink. They did also comment that the bottom of the Challenger Deep consisted of diatomaceous ooze – a form of microalgae. 

Unexpectedly, they also managed to communicate with the ship on the surface using a sonar/hydrophone voice communications system. The messages took seven seconds to travel to the surface, meaning it was travelling around 1.6 km/s (one mile per second). 

After twenty minutes, the crew onboard the Trieste released the hoppers and slowly the vessel began to climb – a journey that would take them 3 hours and 15 minutes to reach the surface. The Everest of the Oceans had been conquered.  

Where Nobody Has Gone Before 

The achievements of the crew and the Trieste cannot be overstated enough. This was a trailblazing expedition that almost doubled the previous world record set years before. In fact, in just twelve years a series of bathyscaphes had revolutionized deep-sea diving and effectively conquered depths that many had thought impossible for humans to survive in. As the two men descended to the Challenger Deep that day, they not only gazed out at these depths for the first time but reestablished the limits of human possibility.  

And the fact that this was all done without the modern technology used on today’s deep-sea submersibles makes it all the more astonishing. This was an old-fashioned, swashbuckling scientific adventure at its very best. 

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