1980s Sinn U-Boat Titanium (Ref. 8820T) W/ Box

Sinn was founded in 1961 by flight instructor and pilot Helmut Sinn under the name ‘Helmut Sinn Spezialuhren’. While a relatively young company, Sinn retains deep roots in aviation and aviation-related timekeeping, but has also expanded the brand to offer other functional timepieces and sports watch designs.

The Sinn U-Boat Ref. 8820T is a fascinating and rare dive instrument from the 1980s, notable for being among the first Sinn models to feature a lightweight and corrosion-resistant titanium case. Designed for professional use, this watch incorporates a unique analog capillary depth gauge, visible just inside the bezel. The inner rehaut features a depth scale calibrated from 0 to 150 meters, with readings flowing clockwise from the 3 o’clock to the 2 o’clock position — an innovative and highly legible layout that made this watch a serious tool for divers.

Examples with a red or yellow “U-Boat” logo above the 6 o’clock marker are especially collectible, believed to be limited editions produced specifically for the Asian market, likely Japan. These dials add a rare visual cue that sets them apart from standard production models.

The 8820T continued in production into the 1990s and remained in the catalog after Sinn’s acquisition by Lothar Schmidt in 1994, though later versions were updated with a sapphire case back and the removal of the depth gauge, marking early examples like this one as particularly desirable for collectors of Sinn’s most functional and forward-thinking designs.

A true artifact of Sinn’s experimental era, the 8820T is not only a diver’s companion but a significant piece of horological history.