How far H-class construction really progressed

Is it accurate that machinery work began for the H class but only about forty feet of keel steel was assembled?

Some yard work probably began, but its extent remains disputed before the yards shifted toward submarine production.

Claims that machinery work began and only about forty feet of steel were assembled remain disputed. The working judgment is that the major yards probably started something after Bismarck and Tirpitz. How much progress they made before turning to mass submarine construction is uncertain. The competing interpretations do not support a precise construction extent.