The failure of wartime flak submarines frames the basic trade-off. French and Russian boats later carried surface-to-air missiles around the sail, giving them a way to threaten an anti-submarine helicopter or patrol aircraft. Firing usually meant the aircraft had already found the submarine, and the engagement advertised rather than protected its position. The concept could complicate an aircrew's hunt, but it exchanged concealment for a last-ditch defensive shot.
Notable Point · 27:34-28:10
Why anti-aircraft submarines sacrifice their best defence
Flak submarines and later sail-mounted missiles could threaten patrol aircraft or helicopters, but fighting back exposed a boat that survived chiefly by remaining hidden.