a 1941 gun duel between a merchant and U-boat

[TorpX]

Well it worked for U-69! They were clearly weaker gunwise, but that did not matter after the surprise attack from close range.

I'm thinking that U-69 was too close for the guns of the Robert L Holtto be brought to bear; that is depressed enough. The U-69 article stated they closed to less than 800m before firing, so it sounds like most/all of the ships guns were useless in this situation.