>>723144621
It's a pretty incredible operation
>Preliminary Operations involve using the Corsairs to raid Gondor's coast and pin down the regional forces while using forces from Mordor and Minas Morgul to probe the Gondor's strongholds on the River Anduin
>Main operations begins by capturing Osgiliath with an amphibious assault to repair the main bridge crossing while a northern army out of the Black Gate takes Cair Andros, ensuring multiple crossing points are available.
>Outer fortifications are breached (using gunpowder, take that Saruman). Part of the force marches North on the road to block any attempt to relieve the siege by Rohan.
>Main assault begins. Assault includes specialized siege weapons (like Grond) because Minas Tirith's outer wall is probably too strong to blown up with black powder (Sauron was right).
>Southron Cavalry and Oliphants are kept far back in reserve since they can't participate. They are kept far enough back so that any disruptions to the main assault force won't result in a rout and they can instead act as a rallying point for the main army (which is exactly what happens).
It's a very well thought out and competent plan. And Sauron wasn't even going to launch it when he did. But he thinks Aragorn has the ring and desperate to eliminate Gondor before Aragorn can unlock its secrets. Unfortunately the blocking army is bypassed by Theoden thanks a secret route only the Druedain know (not even the Gondorians know of it) and Aragorn is able to rally Gondor's regional forces with the army of the dead scaring off the Corsairs, and arrives just in time with some very favorable winds (ie divine intervention).

Meanwhile, as >>723144841 points out, Saruman's attack on Rohan is a complete clusterfuck of a Hail Mary throw because he has run out of time, lost the ring, and Sauron is aware of his treachery.