A monocoque case is a watch case whose middle part and back are made as one piece, so there is no back to remove. With no joint at the back, it needs no caseback gasket. That removes one place where water could get in. It is used mainly on dive and sports watches.
How is the movement fitted in a monocoque case?
A monobloc case is typically cut from one solid block of metal, with the back built into the case. Because there is no back, the movement goes in from above, through the crystal side. A traditional case works the other way. Its back is a separate part that is screwed or snapped on, and the movement goes in from the rear. To reach the movement in a one-piece case, a watchmaker usually takes off the crystal, the bezel or both. The movement is then lifted out from the top. All servicing happens from the front.
Where it comes from
The word comes from vehicle building. Mido introduced the monocoque case with its Ocean Star in 1959. At the time it was seen as revolutionary because it removed the water-resistance problems of casebacks. At the 1963 Swiss Watch Fair, Tissot’s new Seastar Seven used the same construction. Its case was made as one unit and the movement was fitted from the front. Seiko’s 1968 diver’s watch had a one-piece case with no separate back and was water resistant to 300 metres. Omega’s 1970 Ploprof, a Seamaster Professional 600 rated to 600 metres, is another example.
How is it different from other water-resistant cases?
A two-piece case with a separate back is not a one-piece case, however water resistant it is. Not every front-loading case is a one-piece case either. What matters is whether the back and the middle are a single part. The design has trade-offs. It gives more stability for less weight, but it is harder to make. It is also generally a poor choice if you want a display back that shows the movement.
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