Dönitz in his memoirs (Ten Years and Twenty Days; The World Publishing Company, Cleveland and New York, 1959) titles the chapter about the Norwegian campaign: "The Norwegian Operation and the Torpedo Crisis"

The most notable quote:
>On April 16 at 0410 Prien reported that he had come upon transports lying at anchor in Bygdenfiord and had fired eight torpedoes at the long wall of ships, motionless and overlapping each other - but without achieving any success.
He gives an account on reported failures, among them the aforementioned Warspite accident. Some misses, some did not fire, some fired prematurely. Some events are described in detail, what was the plan, data of ranges and such.
He concludes that both contact and magnetic pistols caused malfunctions. And not just the incapability for detonation, or the early explosion, but some torpedoes run deeper than set depth, and this caused some of the misses too.
It is hard to judge - from this glance I took - the extent of possible destruction if they had adequately working torpedoes. Would be good to know what British ships were there, and in the crosshairs of the optics.