Sinn U-Boat Titanium (Ref. 8820T), 1980s

Dealer description — Craft & Tailored

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. SPECS Stock # SINUB8820 Brand Sinn Style U-Boat Dive Watch Model 8820T Serial N/A Size Men's Material Stainless Steel Dial Matte Black Millimeters 39 Bracelet Sinn Titanium Bracelet CASE & BRACELET The unique titanium case is in wonderful overall condition, showing honest signs of light use throughout, with all of the factory dimensions and geometry fully present. The titanium unidirectional bezel is also in excellent condition, retaining its tritium triangle with minimal signs of previous use present. The case retains its original screw-down crown at 4 o'clock. The titanium case back exhibits some signs of rubbing from being previously worn on a Nato strap for a period of time, though all the factory markings and engravings remain fully present. The bracelet is a later unit used for the 8820 model, and it fits the watch perfectly, retaining 13 links that show almost no stretch and will fit up to a 7.25-inch wrist. DIAL & HANDS The matte black "U-Boat" dial is in virtually perfect condition, showing no age or damage. The tritium lume plots have achieved a beautiful golden-yellow patina and show no degradation under UV light inspection. The original tritium hands have aged a shade lighter than the dial and exhibit very minor spots of lume loss in the hour and minute hands, but remain stable when inspected under UV light. ACCESSORIES The watch comes with its original Sinn box. The watch is keeping time, but the service history is unknown. A movement service can be provided upon request.