In 1940, Britain had a problem that courage alone could not solve. The country was at war with Germany, and almost everything it needed to keep fighting had to cross the Atlantic Ocean. Food, fuel, ammunition, airplane parts, trucks, raw materials, and even the basic supplies needed to keep civilians alive depended on merchant ships making the trip from North America to British ports.
Germany understood that perfectly. Instead of trying to defeat Britain only in the air or on land, German U-boats began hunting the ships that kept the country alive. They waited along the shipping lanes, often attacking at night, slipping toward convoys and firing torpedoes into slow-moving cargo vessels.
For the men aboard those ships, the Atlantic could be terrifying. Convoys moved slowly, sometimes through brutal weather, while escorts searched for submarines that were often invisible until it was too late. A torpedo could hit without warning, turning one ship into a fireball while the rest of the convoy was forced to keep moving.
The losses became staggering. Between 1939 and 1945, thousands of Allied merchant ships were sunk in the Atlantic. Winston Churchill later wrote that the U-boat threat was the one thing during the war that truly frightened him. Germany did not necessarily need to invade Britain if it could simply starve the country of everything it needed to continue fighting.
Britain and its allies responded with escorts, sonar, radar, aircraft, and increasingly sophisticated convoy tactics. But there was another part of the solution that was much less glamorous. They needed more ships, and they needed them faster than anyone had ever built ships before.
By the time the United States entered the war, the problem had become almost brutally simple: Germany was sinking cargo ships at an enormous rate, so the Allies needed to build them faster than the Germans could destroy them.
That requirement produced one of the great industrial achievements of World War II: the Liberty ship.
Liberty ships were not designed to be elegant, and they were not especially fast. They were big, slow cargo ships built around a simple idea: standardize the design, simplify the construction, and build as many of them as humanly possible.
Instead of constructing every ship piece by piece in the traditional way, enormous sections could be fabricated ahead of time and then brought together at the shipyard. Welding replaced much of the slower riveting that had traditionally held ships together, and workers who had never built ships before could be trained to perform specific jobs on an almost assembly-line scale.
Henry Kaiser became one of the central figures in the effort. His shipyards attacked shipbuilding the way automobile manufacturers attacked cars. Anything that could be standardized was standardized, anything that could be prefabricated was prefabricated, and every unnecessary delay became a problem to solve.
The results were ridiculous.
In November 1942, workers at Kaiser’s Richmond, California, shipyard decided to see just how quickly they could build one. At one minute after midnight on November 8, they laid the keel of the SS Robert E. Peary and immediately went to work.
Huge prefabricated sections of the hull swung into place from cranes. Deckhouses arrived already fitted with bunks, wiring, and equipment. Hundreds of workers rotated around the clock as the ship seemed to rise almost overnight from the yard.
Four days, 15 hours, and 29 minutes later, the Peary slid into San Francisco Bay.
A 441-foot cargo ship made from roughly 250,000 parts had gone from keel to launch in less than five days. It sailed for the South Pacific shortly afterward carrying food and war supplies.
That particular build was a publicity stunt, but the larger accomplishment was very real. American shipyards eventually built 2,710 Liberty ships, and by 1943 they were completing them at a pace of roughly three per day. They carried tanks, airplanes, ammunition, food, fuel, and nearly everything else necessary to wage a war across two oceans.
The strategy worked. The Allies were getting better at protecting their convoys, but just as importantly, they were producing merchant ships at a rate Germany simply could not match.
Then some of the ships started cracking.
At first, the failures were strange enough to be dismissed as isolated problems. A crack might appear in the deck or along a welded seam. In other cases, the damage was much more serious, with fractures running through large sections of a ship.
A few vessels broke completely in two.
That was not supposed to happen. These were steel ships. The steel had been tested, the material met the specifications engineers were using at the time, and the ships were designed to withstand the enormous forces of ocean travel.
Yet something about them was failing, and the problem appeared particularly often in cold water.
Investigators eventually began to understand that the question they had been asking about the steel was incomplete. They knew whether the steel was strong. What they had not fully appreciated was whether it was tough.
Those sound like the same thing, but they are not.
A material can withstand a tremendous amount of force and still behave badly once a small crack forms. In warm conditions, steel may deform around that crack and absorb some of the stress. But certain steels become much more brittle as temperatures fall.
Now add another part of the Liberty ship design: welding.
Older ships had typically been riveted together. If a crack began moving through one plate, it would often encounter a riveted joint and stop. A welded Liberty ship could behave differently because large sections of the hull were continuous.
Once a crack began, there might be very little to keep it from continuing through the steel.
Corners around large openings in the deck created another problem because they concentrated stress. A small defect that might have remained a small defect under different circumstances could suddenly become the starting point for something much larger.
The Liberty ships had been tested for strength, and the steel had passed those tests. The problem was that simple strength was not the whole story.
The failures helped drive a much deeper understanding of fracture toughness: the ability of a material to resist the growth of a crack once one already exists. That work eventually influenced how ships, bridges, buildings, and countless other structures were designed and tested.
There is a financial lesson buried in that distinction.
Most financial plans get tested for the things we already know how to measure. We run retirement projections, calculate historical returns, look at diversification, and estimate how much someone can reasonably spend. Those are useful tests, just like measuring the strength of steel was useful.
But strength and resilience are not exactly the same thing. A portfolio might look great during normal markets but depend heavily on one company. A retirement projection might work beautifully as long as spending stays near the assumption. Someone might have plenty of assets but very little cash available when something unexpected happens.
None of those things necessarily means the plan is bad. It just means that every so often, instead of asking whether a financial plan is strong, it may be worth asking a slightly different question:
Where does the crack stop?