Circular-running torpedoes and failed marks

Did the Royal Navy or other Second World War navies suffer runaway torpedoes and circular runs?

Yes. Italian experiments with homing and circling behavior mixed deliberate ideas with accidents, while torpedo failures across navies sometimes ended a design before production.

Torpedo development cannot be judged only from successful service weapons. Italian work on homing or circling behavior produced both intentional experiments and dangerous circular runs, and other navies also encountered serious torpedo faults. Some marks never reached production precisely because testing exposed unacceptable behavior.