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Case

Soft-iron inner cage

Probable

An inner case of soft iron enclosing the movement and shunting magnetic flux around it, fitted to the Mark series and the Big Pilot. It is the reason those watches meet a navigation specification, and it is a CASE feature rather than a movement one — the caliber inside is not itself antimagnetic.

Part reference

Brand
IWC
Material
Soft iron
Identifying marks
A solid caseback rather than a display back, because the cage must be closed to work. The inner cage is visible only with the movement out; its practical signature is the absence of a display back on a reference that would otherwise be expected to have one.

Documented variations

Classification

FactoryDocumented as shipped from the factory for this reference and period.PeriodNot original to this watch, but correct for its production period.ServiceFitted by the manufacturer's own service network. Not a defect.AftermarketThird-party part. Affects originality, not authenticity.ModifiedGenuine parts in a configuration the factory did not sell. Affects originality and value, not authenticity.CounterfeitDeceptive reproduction intended to pass as genuine.UnknownEvidence on file does not settle the question.

  • Cage present, solid caseback

    FactoryProbable

    Whole production

    Correct on the Mark series and Big Pilot. A display caseback on a reference specified with a soft-iron cage is a contradiction: the watch cannot have both, and one of the two claims is wrong.

  • Cage removed or absent

    UnknownProbable

    Whole production

    A watch that has lost its inner cage has lost the property the model exists for. A case finding rather than an authenticity one, and one worth reporting because it is invisible from the outside.

Documented on these references

  • IWC 6B/346Factory

    Whole production

    The cage is why the watch met the Air Ministry's specification. A Mark XI with a display back has been modified and has lost the property it was issued for.

  • IWC IW328201Factory

    Whole production

  • IWC IW500901Factory

    Whole production

Provenance of this record

Sources & Evidence

Primary sourceManufacturer documentation

IWC — collection and caliber specifications

IWC Schaffhausen

Accessed
2026-08-18

Cited for

This referenceHigh confidence
View source ↗
Secondary sourcePhysical examination

Research on IWC military-issued watches and Air Ministry markings

Institutional and collector research over issued examples

Accessed
2026-08-18

Cited for

This referenceProbable

Last verified: Not yet reviewed