U-Boat Watch Darkmoon 44 Imperial Blue IPB 8700/B. A collection inspired by the dark side of the moon. The U-Boat watches Darkmoon goes beyond the boundaries of traditional design, combining innovative features with retro style lines. The Swiss electromechanical movement is completely immersed in a low viscosity lubricating oil. The oily liquid flows into the dial making it an absolute and deep black and creates an ever moving compensation bubble that surprisingly amplifies view of the hands that seem to flow free as in the absence of the glass. Different shades of dial with Soleil finish. Oil Immersion concept. Innovative system of battery replacement and of Oil Refill.