Marconi Internal Company Documents & Photographs

2 Folders marked Marconi containing images of their Sounding Apparatus, showing the apparatus mounted aboard ships, some images with dates putting the folders between 1935 and 38.

Sounding the Depths: Marconi’s Glasgow Work on Echo Sounding, 1935–1938

In the final years of his life, Guglielmo Marconi became involved in a quieter, but still important, chapter of marine science. Between 1935 and 1938, he and a team of engineers were working from Glasgow on the development of deep-sea echo sounding — a method of using sound pulses to measure the depth of the ocean. While Marconi is best known for wireless telegraphy, this lesser-known work marked a shift in focus: from sending signals across the sea, to exploring what lay beneath it.

By the mid-1930s, Marconi’s company had a number of engineering centres across Britain. Glasgow, with its strong links to shipbuilding and marine industries, became a useful base for developing and testing equipment at sea. The River Clyde and the surrounding shipyards gave the engineers access to vessels for trials, and the region already had experience with marine electronics.

Marconi himself remained active in the company’s direction until his death in 1937, though much of the day-to-day work on echo sounding was led by his technical staff. The Glasgow division, in particular, became focused on improving how ships could measure the depth of water beneath them using echo technology — bouncing sound waves off the seabed and timing how long it took for them to return.

The idea of using echoes to measure depth wasn’t new by the 1930s, but the technology was still in its early stages. The Marconi engineers were working on making it more accurate, easier to install, and more practical for everyday use on ships.

Some of their key developments included:

• More reliable transducers, to send and receive sound pulses underwater.

• Better signal amplification, to pick out the echo from background noise.

• Simpler displays, so ship crews could read depths in real-time from paper traces or dials.

They also worked on ways to calibrate the devices correctly, taking into account variables like water temperature and salinity, which can affect how sound travels.

Trials were carried out on various vessels operating in and around the Scottish coast and further out into the Atlantic. These tests helped refine the equipment and gave ship captains a practical way to measure depths without using traditional lead lines.

There were two main reasons why this work was important. First, commercial shipping companies were increasingly interested in safer navigation, especially around tricky coastlines or in poor weather. Echo sounding gave ships a way to avoid running aground — and it worked whether or not visibility was good.

Second, and more quietly, the Royal Navy was already thinking about submarines. Knowing what lay below was just as important as knowing what was on the surface. Echo sounding played a role in early submarine detection systems and in mapping the seabed for naval planning.

In fact, although Marconi wasn’t directly involved, the British Admiralty’s HMS Challenger II used similar technology in 1938 to measure the depth of what became known as the Challenger Deep — the deepest known part of the ocean. This was just one example of how rapidly echo sounding was becoming a key tool in both science and strategy.

Marconi died in 1937, before much of this work reached its wider audience. But his role in supporting and guiding the development of echo-sounding technology during the Glasgow years should not be overlooked. The Marconi Company continued to supply marine echo sounders to commercial and military vessels through the war years and beyond.

In the years after the Second World War, the same basic technology formed the backbone of deep-sea exploration, undersea cable planning, and even oil and gas prospecting offshore.

Although he’s remembered first and foremost as the pioneer of wireless, Marconi’s late-career work — and the efforts of his team in Glasgow — helped open up a new era in how humans study and navigate the oceans.

• Collins, R. Marconi’s Legacy: Wireless Communications and Beyond. Macmillan, 1981.

• Simmons, J. "Echoes from the Deep." Journal of Maritime Technology, vol. 6, no. 2, 1995, pp. 45–59.

• National Archives (Kew): Marconi Marine Correspondence, 1935–1938.

• Royal Navy Hydrographic Office reports, 1936–1938.

• Howse, D. Greenwich Time and the Longitude. Philip Wilson, 1993.