On the south-eastern underbelly of the Massachusetts shoreline, overshadowed by the hook-shaped peninsula of beautiful Cape Cod and the harbour islands of Nantucket and Martha’s Vineyard, New Bedford is the kind of place most visitors drive right through.

All but forgotten on the Acushnet River, the downtown is a relic of its 19th-Century heyday, preserved as a monument to history and a peculiar reminder of the city’s rise and fall. The quaysides and cobbles still buzz with local life, but scratch below the surface and darker, more uncomfortable truths lurk on every corner.

Because New Bedford isn’t just any town. On a visit, you’ll learn it was once the wealthiest city per capita in North America. But you’ll also hear it was where men were 100 times more likely to die than anywhere else and that the streets were once overrun with blubber and blood. The catalyst? Whaling.

National Park Ranger Andrew Schnetzer walks visitors through this murky history several times a week, chewing over the divisive, taboo and controversial subject. First, he takes them down William Street, site of the red-bricked New Bedford Whaling National Historical Park headquarters. Then to Water Street, once wall-to-wall with candle works, coopers, carpenters, shipwrights, blacksmiths, oil refineries, insurance companies and the richest banks on the continent.

“We call New Bedford ‘the city that lit the world’ for a reason,” Schnetzer told me, pointing to what was once the most profitable street in the US. “The Quakers – the religious dissidents who first settled the area – found that if they rendered the fat from a whale carcass washed on shore, then lit it, they had smokeless, scentless, beautiful lamp oil.”

As gruesome as it sounds, whale oil was a plentiful resource, and within years the operation had multiplied tenfold. To increase yields, liquid spermaceti wax was harvested from the skulls of sperm whales that swam in the channels of Nantucket Sound, then later processed into fuel.

What made it so attractive was that it was cleaner, brighter and worth six to eight times more than regular whale oil. In 1850, for instance, Hadwen & Barney Oil and Candle Factory produced 4,000 boxes of spermaceti candles, plus more than 450,000 gallons of refined sperm oil valued at $300,000 – about $9 million (£6.85 million) in today’s terms. It was a huge profit few argued with. Even if, they say, you could smell New Bedford before you could see it.

The Quakers who first settled the area discovered that whale fat could be rendered into smokeless, scentless, beautiful lamp oil

Within a few generations, the hard-working, parsimonious Quakers had become global titans of the whaling industry, masterminding a business controlled as much by those on shore as on ship. And in the rippling wake, New Bedford was put on the world map.

“At that time, New Bedford was supplying 5,000 street lamps in London,” Schnetzer said, matter-of-factly. “The oil was shipped to Europe, South America and the West Indies, even helping kick-start the American Industrial Revolution. Get in a car today and drive around. The system for making that possible was invented on Water Street. Flick a light switch on in your room, and it’s the same thing. It all began here.”

Today, New Bedford still lives off the deep harbour that empties into Buzzards Bay. Thanks to scalloping, it has the highest value of any fishing port in the US, landing up to 65 million kg of seafood annually. But dig deeper, and the whaling story remains writ large on the streets. The Moby-Dick Brewing Company is on the corner of Union Street, while the faux-historical Whaler’s Tavernis next door. Running parallel on Johnny Cake Hill is the clapboard Mariners’ Home (it only stopped housing fishermen in 2006) and, next to that, the Seamen’s Bethel, which continues its mission of remembrance for lost mariners.

New Bedford’s whaling heritage is still writ large on the city’s streets

To escape the rain, Fred Toomey, president of the New Bedford Port Society, ushered me inside the bethel, pointing to a series of wall-mounted marble cenotaphs. Outlined in black, they carry messages of hope, despair and the fate of whalers who perished at sea. Morosely, he recited one aloud, his words echoing across the pulpit.

“In memory of Captain Wm Swain, Associate Master of the Christopher Mitchell of Nantucket,” Toomey read. “This worthy man after fastening to a whale was carried overboard by the line, and drowned 19 May 1844…”

Scholars of Herman Melville’s Moby Dick may recognise this obituary. Particularly because it was an inspiration for the hell-bent Captain Ahab, the monomaniacal seaman at the centre of Melville’s 1851 literary classic. Sit in a pew towards the back and you’ll spy a chalk-scrawled plaque dedicated to the author himself, who visited the bethel before boarding the whaleship Acushnet in January 1841.

Marble cenotaphs on the walls of New Bedford’s Seamen’s Bethel honour the sailors who died at sea

New Bedford’s odyssey began long before Moby Dick, however, dating several decades earlier to 1765 when Joseph Rotch, a prominent Nantucket merchant and his two sons, transferred their substantial holdings to the shore of the Acushnet River, lured by labour and resources. It was a move that forever altered the course of American history.

The Rotches revolutionised the industry. Within one enterprise, they incorporated all phases of activity – from harvesting whales, extracting and refining oil, to distribution using their own ships. They built and outfitted vessels, owned wharves and storehouses, made candles and sold whale oil. In effect, they created the world’s first multinational oil company – a method used by energy corporations today.

Seen on paper, the timeline of the industry’s growth is equally industrious. The first New Bedford whaler, The Dartmouth, was built in 1767, but by 1818 the number of whaling vessels had ballooned to 20, and more than quadrupled by 1828. By 1857, the flotilla peaked at 324, with an annual return worth more than $11 million (about £8 million). The same year, the town was granted a city charter with the Latin motto, ‘Lucem Diffundo’. ‘We light the world’.

In tandem, New Bedford’s waterfront evolved to a bustling commercial port. Wealth seeped from the docks onto the banks, the grid of streets becoming populated by lavishly decorated mansions and rows of patrician homes built on the hillsides. One such mansion, the mustard-yellow Rotch-Jones-Duff House has been turned into a museum, and it is a riot of Greek Revival architecture, balustraded balconies and terraced gardens. It even has a glass observatory so its owner could watch the ships come in without having to breathe in the stinking air.