The Scubacraft SC3 is a fully functional watercraft developed in Wales in the late 2000s and the only prototype of its kind ever built. It attracted interest from the UK Special Boat Service and DARPA before the Spectre production team repainted it matte black and gave it a spot in the underground lab alongside the Aston Martin DB10. Most of what fills Q's workshop in Spectre is pure fiction, beautiful props built to suggest a world of gadgets that don't exist. The SC3 actually works. On the surface, a 160-hp Kawasaki 1,498cc inline four-cylinder jet drive propels it to 50 mph. To submerge, the operator deflates the inflatable tubes in the hull, lets water flood the transom, and the main engine shuts down as four electric thrusters take over, driving the craft to depths of up to 100 feet at 3 knots for up to 90 minutes. Because the SC3 is unpressurized, all occupants wear scuba gear during submersion.…