Also called a diving or diver's watch, this is the major watch category and probably the most recognizable "tool" or sports watch. That is, a watch designed for a specific occupation or activity. Like the field watch, the dive watch was developed to meet a need. Specifically, a watch that could be worn by deep sea and scuba divers at increasingly greater depths and still function.
The first dive watch was the Rolex Oyster. Introduced in 1926, it had a case with a screw-on back and a screw-on crown that sealed the movement off from dust and water – even when the watch was submerged. It gained fame in 1927 when Mercedes Glietze became the first woman to swim the English Channel. When allegations arose that she'd faked the swim, she repeated the feat while wearing a Rolex Oyster as a pendant.
Dive watches by various companies soon developed a romantic reputation – especially when Captain Jacques Cousteau wore one in his feature documentary Le Monde du Silence. The reputation of such watches was set in stone in the 1960s when fictional superspy James Bond wore a Rolex not only in the novels, but in the first 10 Bond thrillers on screen. This formed a cachet that has made such a deep impression on the public that a dive watch is probably the only tool watch that one can wear with a tuxedo.
What sets a dive watch apart is that is designed to not only deal with rough handling, but can also act as a practical timepiece hundreds of feet underwater. In fact, the dive watch is more than a way of telling time, it's a piece of safety gear. Deep sea and scuba dives depend on the diver very carefully keeping track of how much time is spent underwater. If too much time passes when one is more than 33 ft (10 m) down, then nitrogen dissolves in the body tissues and returning to the surface risks the potentially deadly bends unless periodic stops are made on the way up to allow the nitrogen to seep back out.
A dive watch is notable for having a heavy case made of stainless steel or some other tough material that can, by today's standards, withstand pressures of at least 330 ft (100 m) without leaking or compromising the mechanism. Some modern watches are rated to over 3,300 ft (1,000 m) and are fitted with special valves to allow helium to escape during extended mixed gas dives using decompression chambers. Otherwise, the watch might burst from internal pressure when returning to the surface.
The dive watch display is very simple with hands that are designed so that the hours, minutes, and seconds can't be confused for one another and the marks or numerals are large, distinct, and easy to read with luminous chapters.
Then there is the bezel, which is constructed to either lock in place or turn only in an anti-clockwise direction. This allows the diver to keep track of dive time by setting the zero mark over the minute hand when descending or timing a decompression stop. By turning only anti-clockwise, accidentally turning the bezel can only cause the diver to overestimate the time rather than underestimate it – the latter being a potentially fatal mistake.
The other things that mark a dive watch is that the bezel and other components are made to be easy to operate by a diver wearing thick neoprene gloves or with waterlogged, half-numbed fingers. Also, there's either an easily adjustable bracelet made of stainless steel, or a cloth or rubber strap that allows the watch to be quickly fitted over the outside of a wetsuit.