The Waltham A-17 24h military time system

Watch Angels
Watch Angels
Published in
4 min readMar 20, 2023


In the civilian world, the commonly used system for timekeeping is the 12 hour dial where the same notation of time appears twice a day. As a result, the two similar notations must be differentiated with another notation which is AM and PM. This makes it easy to confuse time frames.

In the military world, a slight confusion about time interpretation can be fatal. Therefore, the military had to improvise a time system that reduces any chances of ambiguity. This brought the adoption of the military time system also known as the 24 hour clock system.

Waltham A-17

As world wars progressed, different military forces from different developed nations had to swiftly adapt to change to survive. This brought improvements in strategy and communication. This brought about the adoption of the 24 hour clock in the military. Soldiers in the military often communicated with devices while they were long distances apart to enhance unity and strategies of attack and defense. Due to these, a slight mistake of giving wrong information could cause a wrong move. This was one of the disadvantages of the 12-hour clock system.

For instance, in the 12-hour system, it is very easy to confuse 12 midnight and 12 noon. It was also very difficult in the military to do swift calculations in time difference. For example, in the 12-hour system, it is harder to know that something lasts for six-hour when told it starts from 10:45 to 4:45. On the contrary, it is easier to comprehend that it starts from 10:45 to 16:45. For these challenges in the 12-hour system, the US Navy adopted the 24-hour system in 1920 which was later adopted by the US Army in 1942. But, the 24 hour system was being used unofficially by the Army & Navy during the later years of WWI. Evidence of this can be seen on a small handful of American made WWI trench watch dials.

The United States military later made modifications to their 24-hour system format. They used specialized local time zones. An example is zone J, for instance, 1200J meaning noon (12 PM). They also used hundreds when telling the time. For instance, 1000hrs is read as ten hundred hours, not a thousand hours. Any zeroes must be read when communicating. For example, 0600hrs is read as zero six hundred hours, not six hundred hours. These modifications were made to bring a common understanding of the message sent to all the soldiers of the military.

When Mil Spec MIL-W-6433 was adopted by the United States Air Force (founded 1947) for the Waltham A-17 on March 23, 1951 it did in fact feature a 24 hour dial. This watch was intended as a navigation timepiece for pilots. The A-17 had been in development for several years, since October of 1943, as an upgraded version of the A-11. At the request of US Army Air Corps Pilots radium was to be added to the numerals, 5 minute indices, hour & minute hands and on the tip of the sweep second hand. An auxiliary 13–24 hour track was added to aid in reading military time. The back side of the arrow tipped seconds hand was generally lolli-popped shaped.

The “Lollipop” seconds hand

The 12 hour system is still commonly used in the United States. However, as technology advances the use of the 24 hour clock has been adopted in various areas where mistakes could easily be made. The 24 hour clock is also popular with airline and other transportation systems where misread time could cause confusion. Pilots, scientists and polar explorers have now adopted the 24-hour time system since in most cases, their locations have prolonged sun appearance or darkness. Night time that extends for almost the whole day can disorient an explorer. Disciplines that perform highly sensitive tasks like hospitals and intensive care units also use the 24-hour system to administer treatments. A slight mistake in drug administration can cause death to a patient. The history of military time continues to be written as the world adopts, adapts and tweaks the system for the needs of new technologies and methods.

The Waltham A-17 re-issue will go into presale at the end of March 2023.
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