I think the reasons for removing the Harpoons from submarines were generally:
1. Salvo Size - Using torpedo tubes, a submarine is severely restricted in the number of missiles it can launch at one time. When the TASM was still around, the 688 VLS subs could increase the salvo size (while accounting for different flight times and Time-On-Target), but without VLS you're limited to 4 Harpoons. Against modern anti-missile defenses, those kind of salvos are generally inadequate unless you catch them completely off-guard and unprepared. Add in the fact that the Harpoon is relatively slow (i.e. subsonic), and it's generally just not that effective. The target of Oscars/Charlies were as much lightly guarded merchant shipping as they were carrier strike groups, and against CSGs, the 65 cm wake homing torpedoes would probably have been better weapons in a lot of ways.
2. Targetting - A submarine just can't really generate reliable targetting solutions at anything like 300 miles. Even with convergence zones, they probably can't even sense something on the surface much more than a third of that distance, and I doubt CZ detections could generate anything other than blind fire solutions. A missile with a 300-mile range really needs some form of mid-course/near-terminal guidance. For a ship-launched ASM, some form of airborne platform (organic/friendly helicopter/airplane) provides that guidance. For a sub, they would need a way to coordinate with that friendly platform to confirm that their 300-mile missile gets the targetting and guidance that's needed. Because the US Navy didn't really have the targets (the Soviets were never really a blue-water force), they never really developed the airborne guidance force/doctrine that would be required. Having a slow, subsonic missile just makes it worse because the flight time is just that much longer. I think the USN went with all-torpedoes because torps better match the targetting abilities of the average sub.
So I think some of the debate around US anti-ship missiles misses the point, and revolves more around the idea that other navies have something that we don't rather than it does about tactical needs.
However, I do think the US Navy needs a supersonic replacement for the Harpoon, although I'm not sure that 300 miles is the magic number for range. And I think it's actually a much, more critical need for the surface fleet than for the subs.
When they do get around to building a new anti-ship missile out for subs, I like Mapuc's idea on a torp/missile, sort of like a reverse ASROC, to get some standoff from the launch point.
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