Harbour geography and incomplete torpedo nets shape the attack

The outer harbour held the battleships, while a narrow entrance led to an inner lagoon crowded with cruisers, destroyers, torpedo boats, submarines and a seaplane base. Fuel tanks and their line to the battleship area created additional fixed targets, while anti-aircraft barges and balloon moorings ringed the approaches. A storm had reduced roughly ninety barrage balloons to about twenty. Italy estimated that Taranto needed thirteen or fourteen kilometres of torpedo netting, had acquired about seven and had deployed only four or five. Some netting had become tangled in the storm and needed attention. The deployed nets reached about thirty feet below the surface, roughly the ships' draught, leaving a gap above the harbour bottom. A torpedo with a duplex pistol could run below the nets and detonate beneath a hull, provided its initial water entry did not take it too deep.