Commander C T Suthons
Instructor Commander Cyril Thomas Suthons was a brilliant mathematician, oceanographer, and naval meteorologist whose post-war calculations fundamentally changed our understanding of the ocean.
Beyond his legendary work coordinating the D-Day weather forecast alongside Group Captain James Stagg, Suthons made permanent contributions to marine science and military operations:
Commander CT Suthons Role in D-Day
Group Captain James Stagg’s role was not to personally forecast the weather, but to act as a crucial supreme arbiter. Leading up to June 1944, he presided over an intensely pressured, deeply divided committee of forecasting teams that constantly clashed.
Cyril Tom Suthons, operating out of the Admiralty Meteorological Section, was a key naval voice in these fierce debates. His specialised oceanographic calculations frequently forced Stagg to reshape the briefings given to General Dwight D. Eisenhower.
The Great Clash: Winds vs. Waves
The D-Day forecasting council was divided into three distinct units: Suthons’ Admiralty team, the British Air Ministry, and the US Strategic Air Forces (USSTAF).
In the crucial days leading up to the planned June 5 invasion, the American team (led by Irving Krick) relied heavily on historical analogies and remained aggressively optimistic, predicting clear weather. The British Air Ministry team, looking at raw atmospheric dynamics, was highly pessimistic.
Suthons and the Admiralty team held the swing vote, and their concerns were purely structural:
• The Danger of Wind Force: Allied commanders demanded wind speeds no greater than Force 4 (13–18 mph) for the beach landings, and Force 3 or less in the open Channel for smaller landing craft.
• The Wave Breaking Point: Suthons’ empirical equations showed that even if the wind temporarily dropped, the massive low-pressure systems moving across the Atlantic would generate deep-water swells that would travel straight into the English Channel.
• The Verdict: Suthons’ wave forecasts proved that the waves would be too high for the amphibious Dual-Drive (DD) swimming tanks, which would instantly swamp and sink.
Suthons’ hard oceanographic data backed up the Air Ministry’s pessimism. Faced with this united front, Stagg was able to confidently tell Eisenhower that June 5 was impossible, forcing a 24-hour postponement.
The Alignment: Spotting the June 6 Window
On the evening of June 4, the situation shifted dramatically. The forecasting teams were still arguing over the movement of a cold front, but Stagg noticed a brief, crucial atmospheric pause moving in from the Atlantic.
When Stagg pressed the teams for data on this narrow window, Suthons’ wave-forecasting framework provided the exact answers needed to secure Eisenhower’s approval:
• Calculating the Decay: Suthons calculated that as the storm system drifted northeast toward the Shetlands, the wind direction would shift.
• The “Surf Window”: Using his empirical fetch and duration formulas, Suthons estimated that while the English Channel would still be rough, the waves would decay rapidly enough to allow landing craft to drop their ramps on June 6 without being completely overwhelmed.
Stagg synthesized this critical oceanographic data into a definitive recommendation. Armed with the assurance that the waves would remain just under the catastrophic threshold, Eisenhower gave his famous command: “OK, let’s go.”
The Verification: The Devonport Documents
For decades, the cinematic focus has been primarily on Stagg and Eisenhower. However, the declassification and discovery of the Naval Meteorological Branch Periodical Letters at HMNB Devonport definitively reveals the complex teamwork behind the operation.
These original logs record the frantic 06:30, 17:30, and 21:00 scrambler telephone conferences. They explicitly name Instructor Commander C. T. Suthons alongside Stagg, detailing the complex statistical probabilities and early radar tracking used to calculate the wave limits. The files prove that without Suthons’ precise wave data to ground the debate, Stagg would have lacked the firm evidence needed to guide Eisenhower through one of history’s most high-stakes military decisions.
1. The Pioneer of Modern Tide & Wave Forecasting
Before World War II, forecasting how ocean waves would behave under storm conditions was largely guesswork. Suthons changed this by combining atmospheric physics with advanced mathematics.
• The Suthons Wave Forecasting Method: During the war, he developed mathematical formulas to predict wave heights, lengths, and coastal surf behavior based on wind speed and duration.
• The Invasion Blueprint: His wave models were used to calculate how the English Channel’s fierce swell would impact the flat-bottomed Allied landing craft, ensuring the hulls would not capsize before hitting the beaches.
2. Post-War Discovery of the “Suthons Formula”
Following the war, Suthons continued his research for the Royal Navy. In 1957, he published a landmark paper on oceanic extreme sea levels.
• He developed a statistical method—frequently referred to in oceanography as the Suthons Method—to calculate the probability of severe storm surges and coastal flooding.
• His equations are still referenced today by civil engineers designing modern sea defenses, flood barriers, and tidal gates around the United Kingdom.
3. Legacy in the Royal Navy Meteorological Archives
Suthons’ hand-drawn weather charts, encrypted telephone logs, and statistical probabilities form a core part of the recently declassified files recovered from HMNB Devonport. These logs stand as a testament to a mathematician who used meteorology as a decisive weapon of war.
Wave Heights & The Suthons Method
Wartime wave forecasting was incredibly rudimentary, but Cyril Thomas Suthons pioneered a data-driven approach that bridged the gap between meteorology and oceanography.
• The Suthons Empirical Method: Suthons developed mathematical nomograms (graphical calculation tools) that allowed forecasters to quickly estimate significant wave height and wave length.
• The Core Variables: His calculations relied on three variables: wind speed, wind duration (how long it blew), and fetch (the open distance of water over which the wind blew uninterrupted).
• The Surf Equation: Unlike deep-ocean models, Suthons focused on how these waves behaved as they entered shallow coastal waters. His formulas calculated the exact point where a swell would turn into breaking surf, providing crucial data on whether flat-bottomed Allied landing craft would be swamped or capsized by the Channel’s waves.
Influence on the Mulberry Artificial Harbours
The Allies knew that capturing a heavily fortified French port immediately was impossible, so they engineered a solution: they would bring their own prefabricated, temporary ports—the Mulberry Harbours—and assemble them right on the Normandy beaches. Suthons’ calculations dictated the entire structural engineering baseline of this operation:
• Defining the Design Threshold: The massive floating concrete caissons (Phoenixes) and floating breakwaters (Bombardons) had to be engineered to withstand specific maritime forces. Suthons’ models established the baseline design threshold for the construction teams: the structures were engineered to survive up to Force 6 winds, 2.44-metre wave heights, and 36.6-metre wave lengths.
• the components had to be scuttled and anchored relative to the shoreline to create a calm, protected lagoon for supply ships.
• The Ultimate Test: The accuracy of Suthons’ risk models was proven during the catastrophic Channel Storm of June 19, 1944. The storm generated massive Force 7 to 9 winds and waves exceeding 4.5 metres—far exceeding the baseline safety thresholds Suthons had calculated. While the American Mulberry A was destroyed due to being less securely anchored, the British Mulberry B (sheltered more effectively by natural topography and Suthons’ calculated placement) survived the battering and went on to land millions of tons of supplies.
Instructor Commander C.T. Suthons played a vital role in providing the critical meteorological intelligence that ultimately decided the timing of the D-Day landings.
As a prominent member of the Royal Navy’s meteorological branch, Suthons was part of the specialized weather forecasting team at the Supreme Headquarters Allied Expeditionary Force (SHAEF) in Portsmouth.
His core contributions include:
• Weather Forecasting Coordination: Suthons collaborated closely with Chief Meteorological Officer Group Captain James Stagg and other Allied forecasting centers. They analyzed complex data to find a viable weather window for the invasion.
• Interpreting Environmental Data: He utilized early radar technology, strict statistical probabilities, and scrambler telephone calls to deliver crucial updates directly to Supreme Allied Commander General Dwight D. Eisenhower.
• Delaying and Launching the Invasion: His team’s accurate prediction of a severe Atlantic storm successfully delayed the original June 5 assault, saving thousands of lives. They then correctly identified a brief 24-hour break in the weather, giving Eisenhower the confidence to launch the historic operation on June 6, 1944.
how the team resolved the conflicting forecasts between the British and American meteorologists,
The team resolved their conflicting forecasts through a high-pressure system of intense debate, institutional compromise, and the singular authority of Chief Meteorological Officer Group Captain James Stagg
The resolution relied on several critical factors:
1. Opposing Scientific Philosophies
The conflict arose because the Allied meteorologists were split into three independent teams communicating over scrambled phone lines. They approached the data with entirely different scientific models:
• The American Team: Relied heavily on an “analog method.” They looked at historical weather charts over the past 40 years to find matching patterns, leading them to confidently predict fair weather for June 5
• The British Teams (Dunstable & Admiralty): Including experts like C.T. Suthons, they utilized atmospheric physics and hand-drawn charts. They insisted that Northern European weather patterns were too volatile for long-term analog modeling. They correctly spotted a violent low-pressure system moving rapidly across the Atlantic.
2. The Power of Direct Observations
The gridlock was ultimately broken by real-time data. The British teams had a distinct operational advantage: a network of weather ships, aircraft, and remote stations stationed across the North Atlantic. When these physical assets began recording a severe drop in pressure and rising wind speeds exactly where the British predicted, the American analog model could no longer be defended. This forced a unanimous agreement to postpone the June 5 date.
3. Stagg’s Singular Authority & Diplomacy
While the teams frequently clashed over what would happen next, the ultimate resolution lay in the command structure. Stagg held the sole military authority to deliver the final briefing to General Eisenhower. Under immense personal stress, Stagg synthesized the conflicting arguments, overruled the American push for a lengthy two-week delay, and wagered everything on identifying a narrow, 24-hour “ridge of high pressure