The Breguet Marine 5817BE Automatic Big Date 39mm is a discontinued luxury sports watch that masterfully fuses high-end dress horology with utilitarian elements. Inspired by Abraham-Louis Breguet’s historical role as the official chronometer maker to the French Royal Navy, this specific "BE" variant stands out for its striking two-tone 18K gold construction. It features an 18K rose gold mid-case paired with contrasting 18K white gold lugs, giving it a unique visual identity.
Case Architecture
  The case features Breguet's iconic fluted or "coined" case flanks, which are meticulously finished by hand. It employs heavy, angular welded lugs and wave-shaped crown guards to protect the screw-down crown. The mixed metal configuration places an olive-shaped, high-polish rose gold bezel against silver-colored white gold components for a distinct two-tone look. 
The Guilloché Dial
  The solid gold dial base is hand-decorated using a rose engine lathe to create a mesmerizing, nautical-inspired spiral wave guilloché pattern in the center. The outermost portion features a brushed track adorned with applied 18K gold Roman numerals. Time is read via signature "Breguet" open-tipped hands accented with luminous material for night visibility.
The Big Date Complication
  Positioned prominently at 6 o'clock is the oversized double-date display. Unlike typical date windows that look squeezed onto luxury dials, Breguet framed the aperture with a slight curve that naturally mirrors the round silhouette of the case. The date relies on two separate internal discs to display the tens and units digits individually.
  Visible through an exhibition sapphire caseback, the in-house Calibre 517GG automatic movement powers the watch. The highlight of the movement's aesthetic is its large 22K gold winding rotor, hand-guillochéd in the swirling shape of a nautilus shell. The bridges are finished with crisp Côtes de Genève (Geneva stripes) and meticulously mirrored anglage edges. The movement beats at a modern 4Hz (28,800 vibrations per hour) and features double barrels to deliver a highly reliable 65-hour power reserve.