Torpedo attacks more effectieve than gunfire for enemy submarines in October-November 1939

An item reported that in October 70% of the attacks by enemy submarines were made by torpedoes and 30% by gunfire. The torpedo attack percentage decreased in November tot just 33% despite that torpedo attacks were more effective with 80 against 60% by gunfire. Of the 16 ships sunk in October were 4 defensively armed, of the 7 that escaped 3. In November were 12 ships sunk none was defensively armed but of the 6 escaped 4 were.

Source

The National Archives, Kew Gardens, England CAB-66-4-1 Weekly Résumé (No. 14) of the naval, military and air situation from 12 noon 30 November to 12 noon 7 December 1939.