"Joseph Robert's text on Artillery is on the web, sans illustrations. Henry Larcom Abbot's text is out their on Ebay, but not available through web publication."

Yes, as I noted I have these. Abbot's text is available on Amazon as a Univ. of Michigan reprint, but unfortunately, they don't list Abbot as the author so search on the title (I'll see if I can get them to update that.) Unfortunately, it also excludes the illustrations.

Keep in mind that Abbot suggested thirty 13-inch mortars would be required to keep ironclads from parking close to Fort Fisher. In this case they would be behind an impenetrable and high berm (unlike at McAllister for example.) The 10-inch lacked the requisite punch. (Also note that he says, "and under no circumstances are mortars afloat to be much dreaded.")

Abbot measured accuracy at half a mile with a 10-inch mortar on land. From that he claimed a fairly high hit rate against a boat could be achieved from a single mortar...but notably did not adjust for the loss of accuracy of the even more indirect fire and what amounts to test range aiming (nearly best case.) The firing from McAllister seems to illustrate the problem. At McAllister the range was about a mile for the mortar crews and the orientation was 90 degrees from what Abbot used for his calculations (bow on.) It isn't clear how many mortar rounds total were fired from McAllister at stationary targets, but only one seems to have done any damage. Potentially, around 200 rounds may have been fired for that single hit. (About half of the shots would have been at gunboats outside of the main battery's range.)

Abbot's other smoothbore tests illustrate that the mean impact from center was 6 times greater for a 10" mortar than for large smoothbore guns/howitzers at the same range. That's an area 36 times greater.

I find the theory of torpedo detonation by fire from the fort implausible. The chance of actually striking a torpedo with a round in the water is really slim (the gunners couldn't hit the open gunports on the ironclads at the same range and they could see those.) It seems probable that the firing angle from the fort would result in ricochet at this range anyway. Benton's says that unless the water is choppy a shot striking at less than ~8 degrees will ricochet.

Osbon of the New York Herald reported (he was on board), "While withdrawing from action we passed over three torpedoes, one of which exploded directly underneath our boilers, raising the vessel up bodily and slewing her aground..." The paymaster, Browne, indicates that the rear of the vessel passed near a marker for a suspected torpedo. He doesn't mention any fire from the battery at the time and the battery had earlier shifted its fire to the gunboats. The hole and cracks were bad enough that they ran her aground farther down the river to let the mud stop the flow as she settled in. The garrison commander, Anderson, didn't realize she hit the torpedo and was wondering why she hadn't hit any in steaming back and forth. That suggests he wasn't trying to strike torpedoes with his own fire.

At any rate, Montauk had a leak rate that pumping could not contend with. Relying on the pumps was not the only option. Because she could still beach down stream under the cover of gunboats, even a torpedo hit didn't prove fatal. Granted, most torpedo hits were far more catastrophic...and much worse than what any single 10-inch shot could do...particularly if it was a sand filled shell that would still likely shatter on impact, so that even if it penetrated the deck completely it would have some challenge in causing sufficient and unmanageable damage to the underbelly.