In the foyer of the National Oceanography Centre in Southampton, England, stands a ships painted figurehead. It towers well above head height and depicts an armoured knight with a silver chest plate, a raised visor and a thick handlebar moustache. The knights eyes have a faraway gaze in them and well they might. This wooden statue is the sole remnant of a square-rigged ship that once embarked on a three-and-a-half-year voyage to the furthest corners of the globe, reshaping marine science, unearthing all manner of underwater oddities and permanently changing our relationship with the planets oceans. The vessels name was HMS Challenger.

The journey was no simple A-to-B cruise. Between December 1872 and May 1876, the figurehead on the ships prow felt the salty spray of both the North and South Atlantic Oceans as well as vast swathes of the Pacific, even venturing below the Antarctic Circle. The circuitousness of its route paid off. At the voyages conclusion, one of those on board, the prominent naturalist John Murray, declared it the greatest advance in the knowledge of our planet since the celebrated discoveries of the 15th and 16th Centuries. It was some achievement for a ship that was only ever supposed to be a bit-part in a naval fleet.

Built in Englands now-defunct Woolwich Dockyard and first launched in February 1858, HMS Challenger was constructed as a wooden, steam-assisted Royal Navy corvette, or warship. It measured some 61m in length. Just weeks earlier, the completion nearby in London of Isambard Kingdom Brunels colossal SS Great Eastern an iron-hulled steamship more than 210m long had been reported across the globe. The arrival of the Challenger, by contrast, made a relatively tiny splash. This wouldnt always be the case.

The story of its now-fabled world expedition began 150 years ago, in 1870, when an Edinburgh University professor and marine zoologist named Charles Wyville Thompson persuaded the Royal Society of London to support a lengthy voyage of exploration across the worlds oceans. The idea was a novel one. This was a time when the high seas were considered little more than a hindrance to land-based trade and exploration. Life beneath the waves was largely a mystery. Even Charles Darwin, whose own trailblazing voyage on HMS Beagle had taken place around 40 years earlier, had referred to the oceans as a tedious waste, a desert of water.

Government approval for the voyage was sought and subsequently obtained. The Royal Navy lent the venture a strong, sturdy ship that had spent the first decade of its life on active duty: HMS Challenger. Preparations then began in earnest. Fifteen of the ships 17 guns were removed to make space for on-board laboratories and workrooms. Storage areas were created for the marine samples that would be collected on the trip. A crew was assembled, more than 200-strong and skippered by Captain George Nares, who in 1869 had been at the helm of the first vessel to pass through the newly opened Suez Canal. A team of six scientists, headed by Wyville Thompson himself, joined them.

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By the end of 1872, the revamped Challenger was ready. The ship set sail from Sheerness on Englands south-east coast, on Saturday 7 December. It was leaving behind one of the wettest British winters on record, heading south towards Lisbon and the Canary Islands. Over the following 42 months, the ship would cover around 127,600km on a journey that included no less than 362 stops at intervals as nearly uniform as possible, according to Wyville Thompson to scoop samples from the seabed with weighted nets, study marine life, gauge ocean depths and measure water temperatures.

Thanks to the letters of a young stewards assistant, Joseph Matkin, who was just 19 when the Challenger set off, we have accounts of life on the ship. All the Scientific Chaps are on board, and have been busy during the week stowing their gear away, he wrote on embarkation. There are some thousands of small air tight Bottles, and little boxes packed in Iron Tanks for keeping specimens in, insects, butterflies, mosses, plants, etc. There is a photographic room on the main deck, also a dissecting room.

On-board sustenance, meanwhile, fell some way short of his expectations. I have never been so hungry, Matkin wrote, just weeks after leaving Sheerness. I will tell you what the routine for meals is now: at 6AM Breakfast of Cocoa & hard Biscuit at 11.30, dinner; one day it is salt pork & pea soup the next salt Beef & Plum duff, the next salt Pork again & the 4th Preserved potatoes & Australian Beef in tins if any one can get fat on that in 4 years they must eat more than their allowance.

The findings of the voyage, however, were nothing short of bountiful. The results were later presented in a report that stretched to 50 volumes and 29,500 pages, which gives some idea of the amount of information that was gathered en route. Today, looking through the online collection of its 4,772 physical specimens reveals an extraordinary cornucopia of marine life: sea snails from the Azores; squid from the waters around Japan; tiny filter-feeders dredged from more than 300 fathoms (550m) below the Hawaiian Islands; shark teeth, crabs, sea pigs and snake eels.

These artefacts are today held by museums across the UK, Ireland and the US among them the Natural History Museum in London and the Royal Albert Memorial & Art Gallery in Exeter, England with various items still on display.

Of just as much importance as the specimens, of course, were the thousands of scientific readings the ship was able to obtain by dangling its then state-of-the-art instruments and glass thermometers into the unexplored depths, using long lengths of hemp rope.

The measurements of the Challenger expedition set the stage for all branches of oceanography, explained Dr Jake Gebbie, associate scientist at the Woods Hole Oceanographic Institution, a renowned Massachusetts-based facility dedicated to ocean research. They captured a moment in time that would have otherwise been lost. The report is still used in high-impact research today.

The measurements of the Challenger expedition set the stage for all branches of oceanography

The effect of climate change on water temperatures is just one area in which the voyages findings have proved invaluable. We are currently working on digitising the entire suite of temperature measurements from the Challenger, Dr Gebbie continued, adding that the institute is also seeking to understand the physics that control the ocean on these century-long timescales. Without the Challenger data, he said, this line of research may not have been tractable.

Among its countless other notable discoveries, the expedition was also the first to record the astonishing scale of the Mariana Trench, the Pacific chasm that stretches far deeper than Mount Everest is tall. Indeed, the trenchs lowest point the 10,929m Challenger Deep, a dark abyss of algae-rich ooze and slow-moving flatfish still bears the name of the ship. At the other extreme of human exploration, meanwhile, the ill-fated Challenger space shuttle was also named after the vessel.

The ships journey included port stops everywhere from the Cape Verde Islands and Melbourne to Hong Kong and Yokohama. More often than not, however, its horizons were little more than a rolling, briny blue: a plumbless infinity to be registered and recorded. The voyage was almost inconceivably long, but by the time the Challenger finally arrived back in the UK, on a spring day in May 1876, it was carrying a cargo of scientific contributions that even today continues to shape our understanding of the seas.

But it was more than just a great leap for academia. In the long-term, it was also a voyage that celebrated the oceans and highlighted the rewards of patient sea travel. In his book Endless Novelties of Extraordinary Interest: The Voyage of HMS Challenger and the Birth of Modern Oceanography, author Doug MacDougall includes the writings of one of the ships sub-lieutenants, George Campbell. They give an example of just why, perhaps, the Challengers much-journeyed figurehead, now eternally marooned in Southampton, still stares ahead so intently:

On the night of the 14th the sea was most gloriously phosphorescent, to a degree unequalled in our experience. Astern of the ship glowed a broad band of blue, emerald-green light, myriads of yellow sparkswhich glittered and sparkled against the brilliant cloud below Ahead of the ship, where the old bluff bows of the Challenger went ploughing and churning through the sea, there was light enough to read the smallest print with ease. It was as if the Milky Way, as seen through a telescope, scattered in millions like glittering dust, had dropped down on the ocean, and we were sailing through it.

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HMS Challenger: The voyage that birthed oceanography - BBC News