The external torpedo tubes increased the weight of the first attack but brought manual bow-cap work and vulnerability to damage. Royal Navy planners accepted those drawbacks because the boat might get only one firing opportunity before destroyers forced it deep, damaged it, or drove it away. With a surface speed of about 15 knots, the submarine was not expected to chase a fast enemy task force after it passed the ambush. Its task was to damage, delay, or turn back the enemy so surface forces and carrier aviation could finish the wider battle. Against a movement toward Singapore, even the destruction of supply ships could leave the attacking force too weak to deliver an effective blow.
Chapter · 25:15-27:24
One decisive spread in a full-force plan
External tubes made a heavy first attack possible even if escorts prevented the submarine from firing again.