Less than a century ago, wristwatches—or wristlets, as they were called back then—were considered accessories fit only for women. Real men used pocket watches. And, if the timepiece happened to be gold with a half-hunter case cover, then it would be slipped out on its fob chain a little more often, discreetly on display.

The Anglo-Boer War (1899-1902) was a turning point for wristwatches. Those showy pocket watches were too fiddly for the battlefield, so soldiers took to wearing them on makeshift leather straps on their arms. However, the innovation didn't quite catch on until the end of World War I, when soldiers returned with their timepieces securely strapped on their wrists. Now who could argue against the manliness of a soldier who bravely fought in the war, wristlet or not?

When World War II began, the military demanded more wristwatches for their troops, both on land and in the air. While it is said that no watch house can lay official claim to creating the first pilot watch, there are brands that come close.

Louis Cartier, for example, created a wristwatch for his aviator friend Alberto Santos Dumont in 1904 (but Cartier only started selling the Santos watch in 1911).

In 1929, Longines, together with Lt. Commander Philip Van Horn Weems, designed and patented a watch that allowed the synchronization of the seconds hand with a radio time signal without having to adjust the hour and minute hands. Watches like the Longines Weems allowed pilots to make more accurate calculations while flying.

Breitling started supplying cockpits with chronographs in the 1930s, and then added the circular slide rule to their wristwatches in 1940. This allowed pilots to calculate their current position as well as a future position, based on the aircraft's speed over an elapsed time and distance. They were also able to calculate fuel use and make conversion calculations for time, distance, speed, and temperature values and compass errors. The German government was said to have had five different watch companies making pilot watches for their men during World War II: A. Lange & Sohne, International Watch Company, Laco, Stowa, and Wempe.

IWC also supplied the British army with wristwatches in 1944• Post-war, IWC is credited with creating a niche for high-end aviator watches, which elevated the pilot watch from military workhorse to luxury must-have.

What makes a pilot watch a pilot watch?

Legibility, for one. Pilots needed to read quickly information off their watches in all kinds of situations. The classic pilot watch design features large Arabic numerals, with a triangle flanked by two dots at 12 o' clock (which helps keep the pilot oriented even in low-light conditions). The face is high-contrast—usually white numbers set off by a black dial. The hour, minute, and seconds hands, also had to be legible; in the current crop of watches, the hands, numbers, and other markings are usually coated with luminous substances. Anti-glare treatment on both sides of the crystal minimizes reflection.

Next, the watch has to be easy to use. Hence, large crowns and push buttons enable pilots to manipulate the watch even with thick gloves on. Chronographs help track short periods of time. A flyback function allows the wearer to stop, reset, and start the chronograph with just one button instead of three. The hacking seconds function makes adjusting time more accurate by temporarily stopping the seconds hand.

Other useful features include extra-long leather straps which allows the watch to be worn over a jacket or coat sleeve; GMT or UTC, which makes tracking different time zones easier (particularly useful for commercial pilots); and anti-shock and anti-magnetic features.

These days, those who own pilot watches may not actually fly. But, that doesn't stop them from feeling emotionally connected to these expertly-designed instruments that have their origins on the battlefield.

This story first appeared in Vault Magazine Issue 2 2011.