Lessons in Wristory: A-8 Ground Speed Stopwatch

The best way to describe the market for military watches is probably, “insane”. Collectors love the stories and the purpose-built functionality, and will gladly pay thousands of dollars to get their hands on them. So, as you can imagine, information for military watches isn’t exactly in a shortage. Oddly enough, one of the most mass produced issued watches has a surprising lack coverage, and it’s the A-8 Ground Speed Stopwatch.

Several hundred thousand A-8 stopwatches were made over roughly a decade starting in 1940. Elgin and Waltham were the primary manufacturers during wartime, produced under Army Air Corps Specification 94-27749. Post-war, the spec was re-written as MIL-W-6510 when Aristo, Leonidas, and Federal Television Corp got in on the action.

Produced with 9 or 15-jewel hand-wound movements, the A-8 was designed for navigators to make ground speed calculations while in the air. It featured a black dial and white markings. The outer ring of the dial counted up to 10 seconds and the inner dial located at the standard 12:00 position counted up to 10 minutes of the 10-second revolutions. The A-8 was affectionately known as the ‘jitterbug’ because of the loud and fast ticking of the (very tiny) balance. What’s fast, you ask? 144,000 beats per hour is fast – four times as fast as Zenith’s high-beat El Primero.

Prior to the days of GPS and advanced radar systems, cockpit air speed instruments only told part of the story. For example, let’s say your air speed indicator is reading 200 knots, and there’s a headwind of 50 knots – well, your ground speed is only 150 knots. Since the instrument can only read the speed of the air in which the plane is flying, understanding how far you’ve traveled is an unknown variable.

At lower altitudes, where landmarks are easily identifiable from the cockpit, navigators could use their A-8 to mark time from point to point with the plane’s shadow. For another example, the navigator could pick out two landmarks, five miles apart. As the plane passes the first landmark, he would engage the stopwatch. One minute later, the nav stops the watch as the second landmark flies by. With a quick calculation, the navigator knows the plane is flying at 260 knots. At this point, the air speed indicator readout can actually help give the crew an understanding of what kind of wind they’re flying in.

Bubble Sextant

At higher altitudes, using landmarks becomes very difficult. What the navigators did was use a bubble sextant and navigational charts to help with plotting their approximate location. Through averaging multiple sextant readings with stopwatch timings, navigators could calculate ground speed with a fair amount of accuracy.

One of the most frustrating things about collecting military timepieces is the high cost. But, as luck would have it, the A-8 is very reasonable. They pop up on eBay occasionally, and don’t be surprised if they’re selling for $100 or less. For a primo example with original box and documentation, you can obviously expect to pay more. It’ll likely be impossible to tell if it was used in a bomber, cargo, or transport aircraft, but for the price, it’s hard to beat. If you’re looking to get into the military watch game, the A-8 is a fantastic way to start.

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