Naval weapons that almost reached the sea

Which weapons could major navies plausibly have put to sea in the 1930s, 1940s, or 1950s but did not?

Suggestions include explosive drones, wire-guided and acoustic torpedoes, rocket racks against small vessels, and radar-fed fuze setters, with feasibility and anecdotal-evidence caveats.

An explosive aircraft adapted from the Queen Bee concept could accompany a crewed Swordfish, which would guide it into the target before making its own attack. Another proposal brings earlier experiments with wire-guided Whitehead torpedoes from coastal forts into submarine service, while acknowledging that those early systems had feasibility problems. Further development of acoustic torpedoes is suggested separately. A recollection of Soviet river boats using bombardment rockets against other small craft prompts interest in Katyusha or Land Mattress-type racks against light ships and escorts. The evidence for that antiboat employment is explicitly described as anecdotal. A further suggestion connects radar range data directly to the fuze setter for timed air bursts without requiring a proximity fuze.