Category Archives: Petersburg

Artillery support when the Petersburg mine went off

As you might guess, when thinking of the Crater at Petersburg, a subject which crosses my mind is the use of artillery in the operation.  Not to diminish the other aspects of the battle, but the artillery of the Army of the Potomac played an important role there… and is somewhat overlooked in my opinion.  I’m not an expert in the battle.  So I would direct you to one of many folks who have written book length treatments of the battle.

My schedule has prevented me from writing up more on Petersburg up to this time.  Likely, given the sesquicentennial pace, I’ll have to put that on my “after April 2015″ stack.  But I did want to mention the artillery’s role and provide a graphic depiction, by way of Brigadier-General Henry Hunt’s map:


The map, and a busy map it is, includes a table breaking down by battery the type and number of guns engaged on July 30, 1864:


For those who are squinting, the roll call is eighteen 4-½-inch rifles, two 20-pdr Parrotts, fifty-two 3-inch rifles (3-inch Ordnance or 10-pdr Parrotts), thirty-eight 12-pdr Napoleons, ten 10-inch mortars, sixteen 8-inch mortars, and twenty-eight Coehorn mortars.  Grand total is 164 guns and mortars brought to bear on the Confederate lines in support of the assault.

Some of that number were in the 18th Corps sector and not firing directly in support of the assault.  Others were, likewise, firing on the 5th Corps front well to the south of the crater.  But all were firing at some time that morning to suppress or pin down the Confederates in conjunction with the assault.  For comparison, the “great bombardment” by the Confederates on July 3, 1863 during that “contest” at Gettysburg involved about 140 guns.

Hunt’s map indicates not only the battery positions, but also what the targets were.  This adds to the “clutter” on the map. But this is an incredible resource for determining his intent with respect to the fires placed upon the Confederate lines.


The snip above looks at the area of the mine, and just south.  Notice there are more dashed blue lines leading to the Confederate redoubt south of the mine than there are the redoubt above the mine.  Suppression of the Confederate line was the intent there.

Another Federal position worth noting is that of Company C, 1st Connecticut Heavy Artillery.  Battery number 8 on Hunt’s map contained ten 10-inch mortars.  Circled here in blue.


Those mortars fired on approximately 1,000 yards of the Confederate front, to the south of the crater (blue shading in the snip above).  Recall, these mortars were firing, for at least part of the day, case shot as constructed under Colonel Henry Abbot’s instructions.  Battery Number 19, Company B, 1st Connecticut, with six 4-½-inch rifles, located north-east (center-right on the snip above) of the mortars also covered a large section of the Confederate lines.

One problem with these arrangements is that suppressing fire requires a high rate of ammunition expenditure.  Suppressing fire cannot be sustained, even by a master artillery chief such as Hunt, for longer than a few hours.  At some point, fresh ammunition chests must be rotated in.  The assault had to quickly achieve the initial objectives, or lose the suppressing fire support.

510 wagons, 120 guns and mortars, and six days of work: Siege preperations at Petersburg

On July 16, 1864, Brigadier-General Henry Hunt offered a report to the Army of the Potomac’s headquarters in regard to siege preparations.  The report was somewhat inverse of what one might expect.  Rather than focused on what was being done, Hunt responded to an inquiry as to how quickly the siege preparations might be undone (and materials withdrawn) if the Confederates abandon the lines or the Federals opt to abandon the siege for other reasons.  Sort of the staff work that a good commander (in this case Major-General George Meade) presses.  While the conclusions reached by Hunt are of little use to us today, as not supporting “what if” scenarios of interest, the particulars he offered are worth consideration.  They speak to the magnitude of the effort required to lay siege at Petersburg:

In compliance with the direction of the general commanding to furnish a report as to the time which would probably be required to Withdraw the siege train and material in case it should be desirable, I have to state that the siege material which will be brought into requisition if operations are fully entered upon will be: Forty siege guns, for which must be kept on hand in the magazines for daily supply, 6,000 rounds of ammunition; for 6,000 rounds 100 wagons are required; for 30 mantlets 10 wagons; 40 platforms 40 wagons; implements, equipage, &c., 10 wagons; 20 8-inch mortars 20 wagons; 3,000 rounds of ammunition 60 wagons; implements and equipage 20 wagons; 20 10-inch mortars, &c., 100 wagons: 20 Coehorn mortars and ammunition 30 wagons; total, 410 wagons. Twenty more 8-inch mortars are expected for the siege train, and if received will be used. To move them there will be required another 100 wagons.

To move and maintain the siege batteries – 40 guns, 20 10-inch mortars, 40 8-inch mortars (20 on hand at the time, with 20 more expected), and 20 Coehorns – required 510 wagons. With the number of guns, platforms, rounds of ammunition, and wagons in mind, Hunt calculated the time needed to withdraw the siege weapons… in a round about way:

The loading of the material in order to withdraw it must be done by night, and probably even then under fire. The movement of so many wagons can scarcely be made and the noise of loading heavy bodies finished without being heard by the enemy when the lines are so near, as in this case; nor will it do to sacrifice any portion of the material if there is any prospect of its being needed within a month. But little over half the supply of ammunition estimated for has yet been received, although it is sent forward as rapidly as it can be procured. The time needed to load the wagons will be necessarily much longer than ordinarily required at depots. For instance, the positions of the batteries were not selected with any reference to convenience in this respect, and but few wagons can be brought up at a time or placed in favorable positions for loading, so that the number of men who can be employed at any given place will necessarily be limited. At many of the batteries the inconvenience and danger of providing the daily supply of ammunition will make a system of covered ways necessary for the men who transport it from wagons stationed so far in the rear as to find cover from the enemy’s fire, and also from the approach of the wagons to these points. Time, therefore, becomes the most important element; forty-eight hours would, therefore, be necessary, under favorable circumstances, to remove the material.

And did he get to the point?….. Yes.

I do not think it probable that the entire train could be withdrawn in less than three days.

Hunt went on to say the guns and platforms would be moved last, as to at least give the impression the siege was continuing.  With that, Hunt warned, just in case there were any schemes floating about which pointed in directions other than a prolonged siege:

For these reasons the planting of the batteries should not be commenced until it is determined to carry through the siege operations, or, as an alternative, in case a sudden movement of the army should be deemed advisable, we are prepared to sacrifice a large portion of our material.

Meade forwarded this report to Lieutenant-General U.S. Grant, prefaced with a status report of the siege preparations:

In compliance with your wishes, preparations have been continued for commencing the siege. Batteries are being erected for placing guns and mortars in position to silence the enemy’s fire at the salient on the Jerusalem plank road. The chief engineer estimates that it will take eight days to finish these works and have them ready for their armament. The chief of artillery will require three days to unload the vessels now containing the siege guns, mortars, and materials.

Meade added, for emphasis, a summary of Hunt’s conclusions:

In case of withdrawal, besides the three days indicated in his report for withdrawing these guns, if reloaded at the landing where the vessels now are, Broadway Landing, it would require three additional days, but if they are carried to City Point and there reshipped, this last estimate would not enter into the calculation. I have deemed it proper to lay these facts before you, as they may be material to you in your future plans, and to say that I have directed the siege works to go on and in the course of three or four days shall commence the unloading of the guns and material.

Just some figures to have handy… so to speak.  Six days to break-up the siege and move the materials – at great effort.  Sort of means both feet were solidly in the ring by mid-July 1864.

Meade concluded:

The mine will be ready in a day or two, but will not be loaded or sprung till the effect of our operations against the salient is ascertained.

Digging a shaft under the Confederate position was one thing.  Getting all the pieces in place to take advantage of the planned mine blast… well that was another.  More long days of work were required.

(Citations from OR, Series I, Volume 40, Part II, pages 276-7.)


Shrapnel from mortars: “far more effective than shell in… silencing batteries”

During the Civil War, as can be said for most of the “black powder” age, mortars usually fired one type of projectile – the shell.  There were a few variations, which were mostly incendiary shells.  The main disadvantage to the shell when fired vertically was the need to time the burst in order to achieve a desired effect.  A burst shell did scatter debris, but not in an even pattern.  Its main effect was the blast force, which was limited in area.  A “good” mortar shell burst a dozen feet or less above the intended target.  So at places like Fort Sumter or Petersburg, the practice of mortar fire with shells required the gunners to carefully estimate the time of flight;  translate that to the burn time of the fuse; and make the appropriate adjustments to the fuse, projectile, and weapon.  In the days of paper fuses and black powder, this was not an exact science.

With vertical fire, the force of gravity alone was often sufficient to kill or maim.  Such was the case with stone mortars.  But those weapons, as with shotguns, suffered from poor range.  What the mortar crews needed was some projectile which scattered sub-projectiles about the ground around the target area.  That in mind, some artillerists and ordnance men suggested the use of case-shot from mortars.  In the fall of 1863, then-Colonel Henry Abbot experimented with just such a projectile system at Washington, D.C.:

Knowing that a vertical fire of spherical case shot had been tried in Belgium with a view to dispensing with stone mortars, I applied early in 1863 to Major [James G.] Benton, commanding Washington arsenal, to prepare some projectiles for me in the usual manner, for experimental purposes.  He suggested that the expedient be tried of filling the 10-inch shell with 12-pounder canister shot and adding the bursting charge loose.  This I did in October, 1863; the first time, probably, that spherical case shot were ever fired from a mortar in this country.

The firing was at Fort Scott, in the defenses of Washington, south of the Potomac, the new model 10-inch siege mortar being used.  The target was in a valley fifty yards below the mortar and eight hundred and fifty yards distant.

I’d point out that remains of Fort Scott stand today in Arlington, Virginia, just west of Reagan National Airport.  The valley described was likely Four-Mile Run, south of the fort.

The projectile was the ordinary 10-inch mortar shell with twenty-seven of the balls of a 12-pounder canister (thirty-eight filled the shell) inserted through the fuze-hole, and a bursting charge of 2.5 pounds of powder added on top of them.  The shell weighted ninety pounds and each ball 0.43 pounds, making the total weight one hundred and four pounds.  A charge of one pound six ounces of mortar powder gave a range of eight hundred yards, with a time of flight of thirteen seconds.

For reference, the standard 10-inch mortar shell weighed 98 pounds when prepared for firing.  For the 10-inch Siege Mortar, Model 1861, the standard charge was four pounds of powder to propel out to a range of 2,235 yards.  Abbot used a smaller charge for the tests due to the shorter ranges required.  So one might postulate with a full service charge the case shot might have reached at least 2,000 yards also.

By placing observers at different stations to notice the points at which the shell was projected upon the distant hills, at its explosion, a close estimate of its height above the ground was secured.

Abbot included the results of ten test fires in a table:

Notice the dispersion of fragments reported, and the relation to the height of the burst.  As Abbot noted:

It was concluded from these experiments that when the shell burst, the balls fell in a cone about 30º at the vertex, while the fragments scattered very much more.  The balls had, at this range, ample force to kill, penetrating from three t0 seven inches into turf, where, when thrown by a man with his whole force, they entered less than one inch.  Indeed, a little computation will show that the velocity at impact must have exceeded two hundred feet per second, which, with a projectile weighing nearly half a pound, supplies ample living force to disable man or horse. Of course, if the range were very short the requisite velocity would not be acquired, as it depends essentially upon that of the shell at the instant of bursting.

The fact that the force of the bursting charge is expended in fracturing the shell, and does not materially scatter the balls contained in it, obviates for this kind of projectile the great cause of failure in mortar fire against troops, viz: that if the shell is burst over the point occupied by the enemy, the fragments scatter so widely as to render the position nearly a safe one, unless the shell is near the ground. The uncertainty of fuzes renders this height a matter of practical difficulty to control, especially as the fragments of such shells as bury themselves before exploding do no damage whatever.  The spherical case shot throws its balls evenly over a limited circular space, not exceeding in diameter its height above the ground at the instant of explosion, and hence must be far more effective than shell in retarding the progress of works of siege, or in silencing batteries.  It virtually extends the range of the stone mortar to that of the ordinary shell.

Here we have a “real” secret weapon from the Civil War.   But like all such evolutions, there were drawbacks.  Abbot does not provide the time to prepare the case shot compared to common shells.  Nor does he mention any special handling.  But no doubt the gunners would have been apprehensive about premature bursting of the case shot.  One exploding a few feet from the muzzle might wipe out a  an entire battery.

Silencing batteries?  Well in July 1864, there was a particular calling for such an ability.  And writing this account after the war Abbot mentioned that next:

In accordance with these views this projectile was employed in the battle of Petersburg mine, where General [Henry] Hunt’s orders for the artillery were to use every exertion to keep quiet the batteries of the enemy bearing upon the point of assault.

Yes, how did Hunt employ those 144 guns at the Crater?  A good question… and a good subject for another post!

(Citations from Henry L. Abbot, “Siege Artillery in the Campaigns Against Richmond with Notes on the 15-Inch Gun,” Professional Papers No. 14, Corps of Engineers, 1867, pages 25-7.)