Why Some Countries Use Military Time (And Others Don’t)

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Closeup of the numbers and hands on a clock

In English-speaking countries, including the United States, Australia, and the United Kingdom, people typically use the 12-hour clock, marking day and night with a.m. and p.m. In those countries, if someone were to ask, “What time do you want to meet for lunch?”, it would seem strange to respond, “15:00.” If you did, people might assume you were in the military, as it uses the 24-hour clock, known in the U.S. as military time.

But in many countries around the world, “15:00” would be a totally normal meeting time for lunch, as the 24-hour clock is the standard method of timekeeping. Here’s a look at why some countries go by military time while others split their days into two 12-hour periods.

Two Kinds of Clocks

The 24-hour day originated with the ancient Egyptians, who divided the night into 12 parts based on their observation of rising stars and paired that with 12 daytime periods. So, the 24-hour clock certainly isn’t a modern invention — and nor is the idea of dividing it into two 12-hour periods. After all, when it comes to time, one of the most obvious indicators of its passage is the day-night cycle.

The Middle Ages saw the introduction of the first mechanical clocks, with both 12-hour and 24-hour systems developed at the same time. One of the earliest examples of those clocks was installed in the Dunstable Priory in Bedfordshire, England, in 1283. It was weight-driven and didn’t have a clockface — it was simply set to strike a bell at regular times.

The 24-hour mechanical clock later became established in Italy during the 15th century, and that’s when a split began to emerge. The 24-hour system spread across parts of Europe, while in England a preference emerged for measuring time using two periods of 1 to 12, aka the a.m./p.m. system.

The next big shift happened in the late 1800s and early 1900s with the rise of industrialization. Trains, factories, and military operations needed to run according to a precise, standardized time. This need for greater accuracy drove a shift in timekeeping and a more widespread adoption of 24 hours as the official standard. In 1893, Italy became one of the first countries to officially adopt the 24-hour clock nationally. France followed in 1912, then Denmark in 1916 and Greece in 1917.

Coordinating military operations across time zones in World War I reinforced the need for a standardized timekeeping system, and most European countries adopted the 24-hour clock for their militaries. But while some nations — including the U.S., U.K., and Canada — used the 24-hour clock for military purposes, their civilian populations never followed suit. In the U.S., this divergence gave rise to the term “military time,” which reinforced the idea that the 24-hour clock is used for specialized purposes rather than normal, everyday timekeeping.

Many Countries Use Both

In many countries, it’s not a question of either/or when it comes to clocks. In much of Europe, Latin America, and Asia, the 24-hour clock is the go-to for official, written, and formal contexts, such as train and flight schedules, business hours, TV listings, hospital records, and government documents. But in casual conversation, many people still use 12-hour language — in France or Peru, for example, a person might write 20:00 on a schedule but say, “8 o’clock” in spoken conversation.

Similarly, English-speaking countries use 24-hour time in specific professional contexts even though 12-hour time dominates daily life. Hospitals, emergency services, aviation, and the military use 24-hour notation for precision and to avoid errors, due to the higher probability of getting times confused when using the a.m./p.m. format.

While the 24-hour clock is the international standard format for time today and is currently the most widespread time notation worldwide, many countries use a mix, depending on whether the situation is formal or casual, written or spoken, and official or personal.