Walter Munk was never much of a surfer, but that hasn’t kept him from becoming a legend in the sport. An oceanographer by training, Munk has spent 67 years studying how waves form, how they travel and how they break when they hit the beach. In the second world war, he saved countless lives by helping the Allied military determine when troops could make amphibious landings without being swamped by big surf hundreds of metres from a hostile shore. After the war, Munk’s methods helped surfers find the biggest waves. Today, anyone who checks out a surf forecast on the internet is drawing on his pioneering research.
IN THE summer of 1942, Walter Munk went to the beach. It wasn’t a holiday; Munk worked for the Pentagon and he was there to watch American troops practise for an amphibious landing in north-west Africa. The Allies were losing the war, and the invasion would be their attempt to retake the initiative.
The troops were using boats called LCVPs (Landing Craft, Vehicle, Personnel) – smaller versions of the drop-bow boats that would later storm beaches from Normandy to Iwo Jima. They were not the most seaworthy of vessels. “When the waves exceeded five feet, the LCVPs would swamp,” recalls at the in La Jolla, California. “They would call it a day, and wait for another that was a little calmer.”
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Munk was concerned. “I went back and learned about waves at the landing beaches in north-west Africa. In the winter they exceeded six feet most of the time. I thought a terrible catastrophe was about to happen.”
His commanding officer dismissed his objections. “They”, the officer said, must have figured this out. Today, the 91-year-old Munk is convinced there never was a “they”.
Everyone knew that waves were generated by distant storms, but no one knew where they came from or why, and no one had tried to make surf forecasts. Munk decided to tackle the problem on his own, puzzling out the physics of how storms generate swells and what happens as they hit a beach after crossing thousands of kilometres of open water. A month later, he took his findings back to his superiors. Again they brushed him off.
Luckily, he was stubborn. Before the war, Munk had been studying oceanography, so he took his concerns to his mentor, , then director of Scripps and widely regarded as the top oceanographer in the US. Previously, the two had worked on anti-submarine warfare, looking for ways to help defend North Atlantic convoys from German U-boats. Munk, however, had been born in Austria and Sverdrup had relatives in German-occupied Norway. Partly because of rumours spread by rival scientists, both had trouble maintaining security clearances in the super-clandestine field of anti-submarine warfare.
“Ironically, the US may have inadvertently won the war by denying [them] clearances and getting them out of anti-submarine warfare and into surf forecasting,” says Peter Neushel, a historian at the University of California, Santa Barbara, and an avid surfer.
Despite his security problems, Sverdrup had the clout to get military chiefs to recognise the need for forecasts. He and Munk developed a model but they still needed to test it. “We were desperate to see whether the method was working,” Munk says.
Then they learned that before the war Pan Am had been flying seaplanes on an Atlantic test route between Bermuda and the Portuguese archipelago of the Azores. On each trip, the pilots had recorded the height of the surf. It was a treasure-trove of data.
Sverdrup and Munk hunted down old weather maps, then plugged the weather data into their model to “hindcast” wave heights for each Pan Am landing. To their joy, they found a close correlation with what the pilots had recorded – with one puzzling exception. “Once in a while, the observations showed a big spike which we missed,” says Munk.
Then they noticed that these spikes occurred at evenly spaced intervals – always on Saturday nights, Munk remembers. “We decided they were related more to Portuguese wine than meteorological conditions.”
Reassured, the oceanographers were able to give the thumbs-up for a landing in north Africa on 8 November 1942. This time the army listened, and 35,000 US troops went ashore in calm surf. “I’d say we were tremendously lucky with not-so-good weather maps and not-so-good beach charts,” says Munk.
“This time the army listened, and 35,000 US troops went ashore in calm surf”
Meanwhile, Munk and Sverdrup set up shop at Scripps and began turning out entire classes of surf forecasters. Soon, their disciples were spreading out into the Pacific or teaming up with counterparts in the UK to try to figure out how to predict surf conditions in Normandy, for the long-anticipated D-Day invasion.
The British group, based at the Admiralty’s lab on the river Thames, combined Scripps graduates with a team led by George Deacon, the UK’s top oceanographer. Dubbing themselves “The Swell Committee”, they recruited coastguards to collect as much data as they could about surf in the English Channel. They appear to have met some resistance from the coastguards, who saw their mission as repelling German spies.
Eventually, the Channel model was accurate enough to persuade Allied commander Dwight Eisenhower to postpone the D-Day invasion by a day when faced with weather conditions linked to dangerously high surf.
Sverdrup and Munk’s method of surf forecasting was then used in every major Allied landing in the war. “As we learned more, our predictions became pretty good,” Munk says.
Only once did things go badly wrong. In November 1943 at in the Pacific, landing craft got stuck on a reef 500 metres offshore. When soldiers jumped out with their guns and packs, they found themselves in deep water. Many drowned.
According to most histories, someone misread a tide table and scheduled the invasion for a day when the tide was too low to clear the reef. But Munk thinks no one knew the reef was there. “The major failing was not waves, but beach intelligence. The landing craft ran into an uncharted shoal.”
After the war, Munk’s interest shifted to surfing, which he could watch from his cliff-top home in Southern California. Historically, surfers drove up and down the coast, looking for big waves. Sometimes they found them. Often they heard the frustrating refrain: “Gee, you should have been here yesterday!”
Munk began to ponder where the good waves came from. By studying the way waves spread out as they travel, he was able to calculate that some came from as far as 15,000 kilometres away – farther than the entire width of the Pacific. “There was only one possible answer, which is that they came from the Indian Ocean,” he says.
To confirm this, he borrowed a technique from radio astronomy and set up an array of wave detectors near San Clemente Island, about 100 kilometres off the California coast. The array allowed him to pin down the direction of the incoming swells, confirming that they had indeed originated in tropical storms half a globe away, then spent weeks travelling around the southern tip of New Zealand before reaching California. “Today, every surfer in California is familiar with the fact that the waves come from far away,” Munk says. “At that time, nobody knew it.”
Munk’s one regret is that he missed the potential fortune to be made from forecasts. In the 1950s and 60s, surfing was a small sport, pursued by a few dedicated enthusiasts. Now, surf forecasting is big business. “The question ‘Is there surf?’ is one a dedicated surfer will check every day via or real-time animated film,” says Neushel.
But there remain mysteries in the waves. Surfers know that waves come in clusters, with groups of big ones interspersed with smaller ones – but no one knows why. Nor is it fully understood how waves lose energy over long distances, says Munk. “It’s kind of a puzzle.”
