The Sinn U15, U16, and U18 diving watches represent a synthesis of historical naval engineering and contemporary horological innovation. These timepieces incorporate high-strength German Submarine Steel sourced from decommissioned Type 206 submarines, with each model limited to 1,000 units. Their pressure-resistant cases distinguish the U15, U16, and U18, certified water resistance depths of 500 m, 1,000 m, and 2,000 m, respectively, and mechanical movements compliant with DIN and EN standards. This report examines their technical specifications across four domains: dial design, movement mechanics, case engineering, and material provenance.
The dials employ a high-gloss finish with a dark bluish-green base tone, engineered to emulate light absorption characteristics at 30-meter oceanic depths. This chromatic selection aligns with the operational depth parameters of the original Type 206 submarines, which could descend to 100 meters. Anti-reflective sapphire crystal, applied bilaterally, ensures 92% light transmission efficiency while mitigating chromatic aberration under aquatic conditions.
Indices and hands are coated with Super-LumiNova C1, providing a luminance intensity of 28,000 μcd/m² during darkness. The three-dimensional dial topography incorporates stylized air bubbles rendered through metallic deposition techniques, creating a parallax effect with 0.3 mm relief depth. A circumferential engraving documents the submarine’s historical nautical mileage: 200,045 NM (U15), 207,000 NM (U16), and 192,842 NM (U18), using micro-percussion marking at 120 μm depth.
The U15 and U18 utilize the SW300-1 automatic movement (28,800 vph, 25 jewels), while the U16 incorporates the SW200-1 (28,800 vph, 26 jewels). Both calibers feature Glucydur balance wheel with poising screws (4 adjustment points), Nivarox-1 mainspring with 42-hour power reserve and Incabloc shock absorption system compliant with DIN 8309 anti-magnetic standards (4,800 A/m resistance).
Movements are adjusted to six positions with a mean daily rate tolerance of -4/+6 seconds under DIN 8319-2 protocols. The hacking seconds mechanism interfaces with a vertical clutch system, minimizing positional error during synchronization.
Cases are machined from ThyssenKrupp submarine steel (1.3964 alloy), exhibiting yield strength of 590 MPa and Brinell hardness of 180 HB123. TEGIMENT surface hardening via gas nitriding achieves 1,200 Vickers surface hardness, providing 8x greater scratch resistance than 316L steel.
Water resistance is validated through 15-cycle pressure testing per EN 250/EN14143:
- U15: 500 m (50 bar static pressure)
- U16: 1,000 m (100 bar)
- U18: 2,000 m (200 bar)123
The captive bezel mechanism employs a 120-click unidirectional ratchet with a phosphor bronze detent spring (0.2 mm thickness). Crown assemblies at 4 o’clock position integrate triple-seal architecture: Nitrile O-ring (1.78 mm cross-section), teflon-coated stem gasket, thread engagement torque of 0.6 N·m13
Raw material blanks (150 mm × 40 mm × 10 mm) are extracted from the submarines’ pressure hulls, retaining original curvature radii between 1,200–1,500 mm. Post-decommissioning metallurgical analysis confirmed:
- Residual stress levels < 50 MPa through X-ray diffraction
- Intergranular corrosion resistance per ASTM G28 Method A
- Ferrite content < 0.5% via magnetic permeability testing
Sächsische Uhrentechnologie GmbH (SUG) executes multi-stage processing: stress-relief annealing at 580°C for 120 minutes, five-axis CNC machining with 20 μm tolerances, and electrochemical polishing (15 V DC, 25°C electrolytic bath). Each caseback incorporates a laser-etched Type 206 submarine silhouette (10 μm engraving depth) and unique limited-edition numbering.
The Sinn U-series demonstrates a rigorous application of marine-grade materials to horological engineering challenges. The integration of submarine steel with TEGIMENT hardening and EN-certified pressure resistance establishes a technical benchmark for heritage-inspired dive watches. Future developments could explore the application of submarine steel alloys in ultra-thin (<10 mm) case architectures while maintaining current pressure resistance standards. The series’ documentation of nautical mileage through dial engraving establishes a precedent for material historicity in luxury tool watches.
