Indeed Island #10 was a tough nut to crack. I Don't know about being used for artillery training, but it was located in a position in the river that put the Union gunboats at a bad disadvantage.

However as is the fate of almost all fixed fortifications it did fall to a surprise attack in the middle of the night under the cover of a storm. The Battle of Verdun France 1914 lasted over 2 years, but even those forticiations fell.

Forts Pillow, Thompson and other simular fortifications were not built with the thought of a land engagement and their armaments were directed to the river. Thus they had to be abandoned when Grant's army flanked them with the lost of Forts Henry and Donelson.

From what I have read there was a lot of 32# guns abandoned in these fortifications simply because they could not be removed.

Joe Allport's comments about the movements of the Confederate Infantry at Forts Henry and Donelson is an example of how the Confederate Commanders of February '62 were not thinking. And just how decisive that battle was to the conduct of the war in the western theater, In Tennessee and Kentucky was to be carried forward in the next 3 years.

Now certainly Forts Henry and Donelson were not "earthshaking" as Battles like Shiloh and Gettysburg. But certainly The fall of these Forts in my opinion effected the Battle of Shiloh and may have tipped the scales in favor of Grant in that battle because Johnston didn't have those 12,000 troops who had been surrendered at the forts.

Now it is hard to imagine any battle that cause the Confederacy to lose tactical control over a two state area. Not only that but because of the lost of those 12,000 men at Forts Henry and Donelson, Johnston in an attempt to make up for that lost of manpower order Gen'l Van Dorn to abandon the State of Arkansas and bring his 11,000 man army to Mississippi to make up the difference. That move almost lost the Confederacy the tactical control of the state of Arkansas as well and abandoning the state of Missouri to the Unionist.

To me it is hard to image a battle with more impact than the Confederacy losing all military contol over 4 states of which they only partly regained back that control over only one of them, Arkansas.