Well, there’s a simple answer, and a more thorough one. The simple answer is that a mil-spec watch is a watch that was made for a national government – precisely, for some part of a military force. As with anything watch-related (at least, for aspects that have been around for awhile), there are plenty of details and minutiae hiding in that answer.
So, first off, why a military-spec watch? I mean, aren’t our common (aka civilian) watches sealed up and ready for the abuse? Sure, your G-Shock of today might be up to the task, but in the past, civilian watches really were not ready.
First off, think of the environments that these watches are (or were) likely to face – extreme temperatures, dirt and dust, moisture, and shocks, just to name a few. These watches all needed to conform (at a high level) to three criteria: minimalistic, luminous, and readable. While all three of these can combine into one, let’s take a look at each individually.
First off, minimalism. There aren’t going to be a lot (or any, actually) of unnecessary things found on a vintage mil-spec watch. When it comes to markings, you’re going to have the bare minimum needed to fill out the dial – and maybe not even any branding, plus a secondary 24-hour scale.
All of those markings? They’re very likely going to be luminous (as will be the handset), so readability is maintained, day or night. Of course, the minimal markings ensure things stay “at a glance” readable as well, meaning that the person wearing this watch can quickly get the information needed and continue on their mission.
Of course, these are all criteria that we see in today’s watches as well, to one extent or another. While we not specifically call it out, these are the things we look at in watches that are meant for the outdoors, or fall into broader categories such as field watches, aviators, or divers (which all, of course, trace their roots back to military supplies).
One other aspect from mil-spec watches that carried over to us civilians (as I was surprised to learn), was the matte finishing on cases. This came into being on mil-spec watches primarily for two reasons – reducing reflected light (making the wearer harder to see), and making the case more resistant to the elements it was going to end up being exposed to.
In other words, many of the aspects you probably like in watches today are ones you can find in a vintage field watch, somewhere. If you’d like a more in-depth look at some of the design decisions, and some of the different varieties of mil-spec watches you’re likely to run across, you’ll definitely want to check out this article over at Worn & Wound.