The counterfactual does not require an imaginary defensive system. German torpedoes famously failed against Warspite at Narvik and also failed in an attack on Ark Royal shortly before Courageous was lost. A similar malfunction would leave the carrier alive while still demonstrating how close the anti-submarine deployment had come to disaster. After two warnings, the Admiralty would have a strong reason to stop risking a fleet carrier in the same way before a third attack succeeded.
Notable Point · 1:21:24-1:21:57
German torpedo failures make Courageous's survival plausible
German torpedo failures around Narvik and Ark Royal provide a narrow but historically grounded route by which Courageous could survive her encounter.