Hard hat divers of that period sometimes placed common pocketwatches on the inside of their helmets in order to know the time spent under water.

Like their predecessors early 20th century dive watches were developed in response to meet the needs of several different but related groups: explorers, navies, and professional divers.

After a series of trials undertaken by the Swiss Laboratory for Horology in Neuchâtel in May 1937, the watch was certified as being able to withstand a pressure of 1.37 MPa (13.5 atm), equivalent to a depth of 135 m (443 ft), without any water intake whatsoever.

[4][5] In addition, a large number of "canteen" style dive watches by Hamilton, Elgin or Waltham were made to military specification during and after World War II.

[7] Various models were issued by Blancpain in small quantities to the military in several countries, including US and French Navy combat diver teams.

The Fifty Fathoms was worn by Jacques Cousteau and his divers during the underwater film "Le monde du silence", which won the Palme d'or at the Cannes film festival in 1956, and in the US when TV star Lloyd Bridges wore a Blancpain Fifty Fathoms dive watch in a photo that appeared on the cover of the February 1962 edition of Skin Diver Magazine.

In 1959, the United States Navy Experimental Diving Unit evaluated five diving watches that included the Bulova US Navy Submersible Wrist Watch, Enicar Sherpa Diver 600, Enicar Seapearl 600, Blancpain Fifty Fathoms, and the Rolex Oyster Perpetual.

[11] In 1961, Edox launched the Delfin line of watches, with industry-first double case backs for water resistance to 200 meters.

They later released the Hydrosub line in 1963 featuring the first crown system with tension ring allowing depths of 500 meters.

It was the choice of watch for the character of 007 in the first ten James Bond films, causing the "Sub" to achieve an iconic status.

The watch cases of diving watches must be adequately water (pressure) resistant and be able to endure the galvanic corrosiveness of seawater, so the cases are generally made out of materials like grade 316L or 904L austenitic stainless steel and other steel alloys with higher Pitting Resistance Equivalent factors (PRE-factors), titanium, ceramics and synthetic resins or plastics.

Analog diving watches will often feature a rotating bezel, that allows for an easier reading of elapsed time of under one hour from a specific point.

This saves the diver having to remember the exact water entry moment and having to perform arithmetic that would be necessary if the watch's regular dial was used.

The one minute intervals scale helped with timing the ascent and whatever safety stop the diver deemed necessary.

The dials and markers on the watch face and bezel have to be legible under water and in low light conditions.

For easy legibility most diving watches have high contrasting, non-cluttered dials and markers with a large, easily identifiable minute hand.

[35] None of the tests defined by ISO 2281 for the Water Resistant mark are suitable to qualify a watch for scuba diving.

Movement induced dynamic pressure increase is sometimes the subject of urban myths and marketing arguments for diver's watches with high water resistance ratings.

[38] In 1992, a Comex diver achieved a simulated 701 m (2,300 ft) of seawater depth in an on-shore hyperbaric chamber as part of the Hydra 10 programme.

[39] The watches used during this scientific record dives were Rolex Sea-Dwellers with a 1,220 m (4,000 ft) depth rating and these feats were used in advertising.

[40][41][42] The complexity, medical problems and physiological limits such as those imposed by high pressure nervous syndrome and accompanying high costs of professional saturation diving to depths exceeding 300 m (984 ft) and the development of deep water atmospheric diving suits and remotely operated underwater vehicles in offshore oilfield drilling and production effectively nixed the need for ever deeper non-atmospheric crewed intervention in the ocean.

These practical factors make watch depth ratings of more than 1,000 to 1,200 metres (3,300 to 3,900 ft) marketing and technical show off curiosities.

Normal surface air filled watch cases and crystals designed for extreme depths must be dimensionally large to cope with the encountered water pressure.

An example of these watches is the Sinn UX (EZM 2B), whose case is certified by Germanischer Lloyd for 12,000 m (39,000 ft), which is deeper than the Challenger Deep.

This property endangers a traditional watch case since the crystal would blow out from any significant internal overpressure.

To obtain its water resistance the Sinn UX (EZM 2B) stainless steel watch case has a diameter of 44 mm, thickness of 13.3 mm and the case and bracelet weigh 105 g. This is dimensionally modest compared to air filled diving watches designed for extreme depths.

[50][51][52][53] In January 1960, a Rolex Deep Sea Special prototype diving watch attached to the hull of the bathyscaphe Trieste reached a record depth of 10,913 m (35,804 ft) ±5 m (16 ft) of seawater during a descent to the bottom of the "Western Pool" of the Challenger Deep, the deepest surveyed point in the oceans.

[64][65][66] Two of these watches were attached to the outside of the Deep-Submergence Vehicle Limiting Factor: one on each of the main vessel's robotic arms and an additional one on the ultra-deep-sea lander Skaff.

[68][69] The normal surface air filled watch case is made of (DNV GL certified) forged grade 5 Titanium alloy (same as the hull of the DSV Limiting Factor) has a 55 mm (2.17 in) diameter and is almost 28 mm (1.10 in) thick and has been tested and certified for up to 1500 bar/15,000 m (49,213 ft).

Divers have to inspect their watch and the wrist band for defects before every dive and especially in case it came into contact with dirt, gasoline or strong chemicals, powerful magnetic fields or was banged against something hard during use.