HMS Warspite too was hit by two duds, shortly before leaving the Vestfjorden to Narvik, meaninf after the attack, U-48 claimed two hits, which were duds. "Two metal bumbs were hear in the U-Boat, some twenty seconds or so after launching three torepdoes at the battleship."
Before the actual attack by the Homefleet on Narvik, U-46 was within 600 yards of the battleship, but could not turn in time, to engage, before HMS Warspite rounded a cape, shielding her atainst U-46.
U-48 also had fired two times three torpedoes at the Cruisers of the Homefleet, most likely HMS Penelope and the destroyer Punjabi, or Eskimo, misidentified as cruiser as well. On the 11th of April, U-48 fired twice a salvo of thre at two targets, with the final result that four torpedoes exploded prematurely and two missed. Klt z. S. Schultze compalined that in two days time out of twelve torpedoes fired in all, over half exploded prematurely and the rest missed their mark. "Something was very wrong with our torpedoes", acorcing to his log. After this, Dönitz ordered an investigation on the matter to solve the problems.
See: Haarr, G. H.: "The invasion of Norway, april 1940", ISBN 978-1-84832-032-1