A History and Guide - How to Use a Dive Bezel

Jacob Van Buren

Aug 15, 2025

John Scott Haldane had a problem. Britain’s Royal Navy had commissioned the Scottish physiologist to find a solution for a unique problem facing their divers: decompression. Known since the mid-19th century, decompression sickness (DCS) posed a serious risk for divers and laborers working in pressurized environments, such as caissons. It was his job to develop a set of decompression tables for safe diving operations.

It boils down to how gases act under pressure. When breathing a gas mixture at depth — for the sake of simplicity, we will say compressed air, or approximately 78% nitrogen and 21% oxygen, with the rest being inert gases — the oxygen is used up by the body, and the nitrogen is absorbed into the bloodstream. This build-up will dissolve as it is effectively off-gassed, as it does when each of us breathes here on the surface. Enter pressure. Should a diver undergo a rapid change in pressure, such as by ascending too quickly, the nitrogen will separate from the blood and form bubbles in the tissues and joints. The resulting pain has a habit of contorting its victims, giving DCS its more readily-known nickname of “the bends.”

So why not oxygen?

Pure oxygen becomes toxic after approximately twenty feet, drastically limiting its useful range compared to other gas mixtures. Haldane’s tables proved foundational to establishing safe diving practices. Following the invention of the Aqua-Lung in 1943, recreational diving underwent a veritable boom in the 1950s and 1960s. There was one problem for these new "lung" divers: time.

Enter the dive watch. First introduced in the early 1950s, it revolutionized underwater timekeeping. Divers could accurately track how long they had been in the water in accordance with the no-decompression limit provided by their dive tables. This is important in recreational diving, as a diver should always be able to surface in the event of an emergency without decompression.

But there was a catch. What exactly should a watch for divers be? Early waterproof watches, such as the US Navy’s “canteen watch,” were available for the frogmen of the Second World War, but these watches were flawed. They were only suitable for shallow-water operations and would flood when subjected to the new literal and figurative depths being explored. The parameters were fairly simple — they needed a way of tracking elapsed time during their dives. Take the US Navy trials in 1958, for example. The Rolex Submariner, Blancpain Fifty Fathoms, and Enicar Sea Pearl were tested as commercially available alternatives while they waited for the then-in-development Bulova Mil-SHIPS. While the Rolex and the Blancpain both had bezels, the Enicar did not; yet it still finished ahead of the Submariner due to features that Navy test divers liked.

Combined with a set of US Navy tables and a reliable depth gauge, the dive watch enabled divers to explore depths of over 200ft safely. In practice, its use is simple: upon entering the water, the rotating bezel is moved to the current position of the minute hand. That is it. From there, the diver monitors passing time to stay within their no-deco limit. The tables are then consulted once out of the water to plan a repeat dive, if desired, based on bottom time and a corresponding surface interval.

However, a few issues could occur. The modern standard of a unidirectional bezel was not standard. Many early bezels were friction fit, meaning they could be knocked out of position. On a dive pushing no-decompression limits, this could prove potentially hazardous if one were not paying close attention.

MODERN DIVE WATCHES

Today, dive watches are no longer an essential component of a diver’s kit. They have been supplanted by dive computers, which not only track bottom time and depth but also rapidly calculate the remaining no-decompression limit on the fly — a serious advance over diving traditional tables. If one’s no-deco limit is exceeded, they can even calculate how much decompression is needed before ascending.

This does not mean traditional dive watches no longer serve a purpose. Besides their reputation as rugged timepieces capable of withstanding serious wear, they have another role: vessels for memory. Most divers, besides perhaps those in Garmin’s ecosystem or Apple Watch Ultra users, do not wear a dive computer outside of diving. A dive watch — for many lifestyles — can go anywhere. There is a certain romance to being able to look down at one’s wrist and remember diving a shipwreck 100 feet below the surface in Lake Superior while hundreds of miles away attending to the minutiae of life. And, if you really need an argument for utility, say it’s being used to time a safety stop or a swim cycle during navigation. We won’t tell.

Bulova Mil-Ships

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