The Type V Acoustic torpedo was their best weapon for attack. Second was mines put in places thought to be clear... overnite.
The BMC 1430 lb charge (1943/44)
The EMF influence fire (1939/41/42)
The FMC 90 lb charge , with sinker box to determine exact depth.
All guns were classified as anti-aircraft guns (not ship to ship) and came in 20, 30, 40, and 37 mm depending on model and type (S-80/S-100).
Their biggest enemy was aircraft, and their best defense was speed/darkness.

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Morbius, Morbius! Something is approaching from the Southwest. It is now quite close.