I wonder if the sentry on duty at Hurst Castle gave a second glance to HMS Challenger as she sailed ‘through the Needles, and down Channel with a smooth sea and a light head wind…” on 21 December 1872.

Yet thus, according to the log letters first published in 1881, began a historic marine-research voyage that was to cover almost 69,000 nautical miles – and to revolutionise our understanding of the oceans.

The expedition was led by the professor of natural history at Edinburgh University, Charles Wyville Thomson, who persuaded the British Government to fund the first global marine research expedition and to provide a suitable vessel. HMS Challenger was to fit the bill.

Built at Woolwich Dockyard in 1857, the 200ft ship was a Royal Navy corvette. With her wooden hull and three-masted rigging, she was powered by both sail and steam and had seen naval service in countries as far apart as Mexico and Fiji.

Conversion into a research ship involved the removal of all but two of her guns. In their place came chemistry and natural-history laboratories and a plethora of scientific gear, from bottom samplers and thermometers to 144 miles of sounding rope and a staggering 12.5 miles of piano wire.

Alongside a crew of nearly 250 officers and sailors, under Captain George Nares, Wyville Thomson led the team of six civilian scientists that included naturalists, a chemist/physicist, and an artist. Their mission? ‘To determine the physical, chemical, and biological characteristics of the global ocean, emphasising the deep sea.’

Whether obtaining specimens of marine life and sea water, or investigating the depth, temperature, currents and circulation, and specific gravity of the oceans, the men worked to as regular a schedule as possible. From the Atlantic to the Antarctic and on into the Pacific, the ship zigzagged across the world’s great oceans, stopping off at every continent and sometimes berthing to allow research to be conducted on land.

Along with specimens of some 4,700 new plant and animal species, the team found evidence of invasive species around Hawaii.  Minerals and micrometeorites came under the spotlight, as did the discovery of the Mariana Trench, the deepest point on Earth. Then recorded at a depth of over 8,200m, it is now known to hit 11,034m, in an area later named Challenger Deep.

After the ship returned to England in May 1876, it took a further four years to catalogue the expedition’s ground-breaking findings in 50 weighty volumes, led by on-board naturalist John Murray and laying the foundation of oceanography as a science.

Even today – 150 years later – the results of the expedition continue to make their impact, including underpinning the scientific understanding of global warming.  But what became of the ship?  Plans to convert her to a sail-training vessel came to nothing, and she was finally broken up in 1921.  All that remains is her figurehead, held by the National Oceanography Centre in Southampton.