Sinn Diving Watches

Sinn Diving Watches are the dive line of Sinn, the Frankfurt am Main maker Helmut Sinn founded in 1961. Many carry an EZM number, for Einsatzzeitmesser, German for mission timer. The U models take their letter from the U-boat: their cases are made of the same high-strength, seawater-resistant steel as the outer hulls of the German Navy's Class 212 submarines, an alloy that resists corrosion and magnetism.

The U1 is the reference point. Its 44 mm submarine-steel case is rated to 1,000 m and takes a 22 mm strap, with the screw-down crown moved to 4 o'clock. The bezel is solid metal with milled markings and no insert, and it is captive, so a knock cannot tear it off. Inside is the automatic Sellita SW 200-1 with about 38 hours of reserve. Some versions are hardened with Tegiment, Sinn's process that brings the case up to 1,200 Vickers; the U1 S E pairs it with a black hard coating and ivory lume, a look taken from the U212 S E.

Around it sit bigger and smaller versions. The U2 (EZM 5) was built for navy special forces and is pressure-resistant to 2,000 m. The U212 stretches the formula to 47 mm, the U200 shrinks it to 37 mm, and the T1 and T2 swap steel for titanium at 45 and 41 mm. The U1000 is a 44 mm diving chronograph whose pushers work at depth, and the EZM 3 is a 41 mm diver made to resist shock, pressure and magnetic fields.

The UX (EZM 2B) is the outlier: a quartz watch in an oil-filled case, which makes the dial easier to read under water and rules out a mechanical movement. Germanischer Lloyd certified the case to 12,000 m and the movement to 5,000 m, and the maritime unit of Germany's GSG 9 police force uses it. Limited runs include the U1-D, or Mission Dune, 350 pieces with a matte grey dial and sand-beige details, made for the 35th anniversary of the retailer The Hour Glass.