Maximilian Büsser & Friends’ Horological Machine No4 Thunderbolt (HM4) is unusual but not unexpected: Outlandish designs are precisely what propelled Büsser’s 5-year-old brand (www.mbandf.com) to prominence in the first place. The company’s 43-year-old Swiss founder, who draws inspiration for his timepieces from childhood memories, based the shape of the HM4 on the twin jet engines of the A-10 Thunderbolt II—a U.S. fighter jet that he once assembled as a model airplane. Engine-shaped cowlings contain the watch’s time display and power-reserve gauge at one end and winding and setting stems at the other. Beveled gears transfer energy to the cowlings from the power barrels and escapement on the watch’s horizontal plane. Assembling the first examples of this intricate timepiece, which is available in an initial limited edition of about 20 (a total of 100 will be made available over three years), has proved to be incredibly difficult—particularly the milling of the curved sapphire glass and unibody titanium lower case. This unique, and perhaps unexpected, challenge may explain why the HM4, which debuted in July for $158,000, will go up in price next year.