you have ships offshore to provide artillery support -
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Back when ships actually had artillery - now they are mostly missile armed. Therein lies the problem - arty rounds once fired could not be diverted, intercepted, jammed, or fooled. Missiles have all those weaknesses. Worse, those missiles, by in large, depend on GPS guidance at the moment. Giving up HIMARS is a big mistake, not to mention towed arty.
And what if its NOT a beach landing where they are needed? Just because the current nincompoop that runs them has dome romantic idea how to use them, doesn’t mean the enemy will oblige. This leaves the Marines at the mercy of the AF and the Army for support.
Actually, aside from the aborted Zumwalts, all US destroyers are still equipped with artillery. The new foreign design frigates being brought into service will also retain artillery systems. Also, the Corps is looking to bring in rocket artillery and more missile system of their own to help compensate.
I would point out that if you’re not in a naval or riverine scenario, the Army is probably the better choice to send in the first place.
Also, the Marines didn’t give up HIMARS. They are doubling up on it and are looking for more.