The Swordfish is judged slightly better than the similar-looking B4Y because of its torpedo-release system. A tension wire helped the torpedo enter the water flat instead of diving deeply before settling onto its running depth. That gave the British aircraft an advantage in shallow harbors, rivers and lakes. The B4Y's service in China, including the Panay incident, illustrates the kind of setting in which such a capability would have been useful.
Notable Point · 52:20-53:05
The Swordfish's torpedo-release system helps in shallow water
A tension wire helps a dropped torpedo enter flat, explaining the preference for the Swordfish in shallow-water attacks.