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A bank vault is a secure space where money, valuables, records, and documents can be stored. Vaults protect their contents with armored walls and a tightly fashioned door closed with a complex lock. Vault technology developed in a type of arms race with bank robbers. As burglars came up with new ways to break into vaults, vault makers found innovative ways to foil them. Modern vaults may be armed with a wide array of alarms and anti-theft devices. Some nineteenth and early twentieth century vaults were built so well that today they are almost impossible to destroy. Buildings have been renovated around them. A restaurant in a restored bank building even features a dining area inside the indestructible vault. These older vaults were typically made with steel-reinforced concrete. The walls were usually at least 1 ft (0.31 m) thick, and the door itself was typically 3.5 ft (1.1 m) thick. Total weight ran into the hundreds of tons. Today bank vaults are made with thinner, lighter materials that, while still secure, are easier to dismantle than their earlier counterparts.


The need for secure storage stretches far back in time. The earliest known locks were made by the Egyptians. Ancient Romans used a more sophisticated locking system, called warded locks. Warded locks had special notches and grooves that made picking them more difficult. Lock technology advanced independently in ancient India, Russia, and China, where the combination lock is thought to have originated. In the United States, most banks relied on small iron safes fitted with a key lock up until the middle of the nineteenth century. After the Gold Rush of 1849, unsuccessful prospectors turned to robbing banks. The prospectors would often break into the bank using a pickaxe and hammer. The safe was usually small enough that the thief could get it out a window, and take it to a secluded spot to break it open.

Banks demanded more protection and safe makers responded by designing larger, heavier safes. Safes with a key lock were still vulnerable through the key hole, and bank robbers soon learned to blast off the door by pouring explosives in this opening. In 1861, inventor Linus Yale Jr. introduced the modern combination lock. Bankers quickly adopted Yale’s lock for their safes, but bank robbers came up with several ways to get past the new invention. It was possible to use force to punch the combination lock through the door. Other experienced burglars learned to drill holes into the lock case and use mirrors to view the slots in the combination wheels inside the mechanism. A more direct approach was to simply kidnap the bank manager and force him to reveal the combination.

After the inventions of the combination lock, James Sargent—an employee of Yale—developed the “theftproof lock.” This was a combination lock that worked on a timer. The vault or safe door could only be opened after a set number of hours had passed, thus a kidnapped bank employee could not open the lock in the middle of the night even under force. Time locks became widespread at banks in the 1870s. This reduced the kidnappings, but set bank robbers to work again at prying or blasting open vaults. Thieves developed tools for forcing open a tiny crack between the vault door and frame. As the crack widened, the thieves levered the door open or poured in gunpowder and blasted it off. Vault makers responded with a series of stair-stepped grooves in the door frame so the door could not be levered open. Unfortunately, these grooves proved ideal for a new weapon: liquid nitroglycerin. Professional bank robbers learned to boil dynamite in a kettle of water and skim the nitroglycerin off the top. They could drip this volatile liquid into the door grooves and destroy the door. Vault makers subsequently redesigned their doors so they closed with a thick, smooth, tapered plug. The plug fit so tightly that there was no room for the nitroglycerin.

By the 1920s, most banks avoided using safes and instead turned to gigantic, heavy vaults with walls and doors several feet thick. These were meant to withstand not only robbers but also angry mobs and natural disasters. Despite the new security measures, these vaults were still vulnerable to yet another new invention, the cutting torch. Burning oxygen and acetylene gas at about 6,000°F (3,315°C), the torch could easily cut through steel. It was in use as early as 1907, but became wide spread with World War I. Robbers used cutting torches in over 200 bank robberies in 1924 alone. Manufacturers learned to sandwich a copper alloy into vault doors. If heated, the copper alloy melted and flowed. As soon as the burglar removed the heat, the copper resolidified, sealing the hole. After this design improvement, bank burglaries fell off and were far less common at the end of the 1920s than at the beginning of the decade.

Technology continues in the race with bank robbers, coming up with new devices such as heat sensors, motion detectors, and alarms. Bank robbers have in turn developed even more technological tools to find ways around these systems. Although the number of bank robberies has been cut dramatically, they are still attempted.

Born June 22, 1903 in Indianapolis, John Dillinger was raised by his sister and stepmother. In 1924 he was arrested for attempted robbery and sentenced to 10-20 years in prison. Confinement trained Dillinger as a criminal and leaving prison in 1933, he carried a map of prospective robbery sites. In three weeks Dillinger robbed 10 banks in five states. Known as “Gentleman Johnnie,” he was pleasant and often flirtatious during robberies. The press played Dillinger up as a brilliant, daring, likeable individual, beating the banks that foreclosed on helpless debtors.

Other criminals joined Dillinger, forming the Dillinger Gang. Banks were cased and robberies were timed. The heist was abandoned—no matter what—after a certain amount of time had passed. Getaways were also planned precisely: street lights were timed with back roads and alternate routes noted in the plans. Often, the gangsters didn’t race out of town, they casually motored through back roads. FBI director, J. Edgar Hoover increased the reward for Dillinger and issued agents shoot to kill. The Dillinger pursuit was the largest manhunt in the country’s history.

In 1934, Dillinger’s friend—Anna Sage—agreed to betray Dillinger. On July 22, 1934, Sage, Dillinger, and Dillinger’s girlfriend Polly Hamilton attended a movie on Chicago’s North Side where Federal agents gunned Dillinger down. Following his death, the FBI press announced Dillinger was shot after resisting arrest and attempting to draw a pistol. Other members of Dillinger’s gang were incarcerated or killed in shootouts with police. The reign of John Dillinger and his gang had come to an end. However, Dillinger’s exploits earned him a lasting place in American crime history.


Bank vault technology changed rapidly in the 1980s and 1990s with the development of improved concrete material. Bank burglaries are also no longer the substantial problem they were in the late nineteenth century up through the 1930s, but vault makers continue to alter their products to counter new break-in methods.

At issue in the twenty-first century is a powerful tool called a “burning bar” or “thermic torch.” Burning liquid oxygen ignited by a oxyacetylene torch, this bar burns much hotter than an acetylene torch, getting up to 6,602-8,006°F (3,650-4,430°C). The torch makes a series of small holes that can eventually be linked to form a gap. In the future, the vault manufacturing industry will likely come up with a means to combat the burning bar. Then perhaps criminals will find a more powerful tool, and the industry will change its products again. Vault manufacturers work closely with the banking industry and law enforcement in order to keep up with these advances in burglary.