Category Archives: Mortars

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.

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.)

June 4, 1864: Mortars to the front

Even though June 3, 1864 at Cold Harbor is best recalled as an infantryman’s fight, as mentioned yesterday, the Fifth Corps artillery launched over eighteen tons of ordnance towards the Confederate lines.  While massed batteries, as done with great effect just miles to the south at Malvern Hill in 1862, was not an applicable tactical option, the artillery remained an important combat force on the battlefield.  But field fortifications, even basic trenches, provided some mitigation against traditional field artillery.  With earth and wood protecting the soldiers from direct fire, the infantry could better withstand any eighteen tons of shot and shell the enemy might care to throw over.

Increasingly, not just in the Civil War but across the scope of warfare, vertical fires became more important where fortifications came into use.  In the Second Corps sector of the Federal lines, mid-day on June 3, Colonel John C. Tidball employed Coehorns in close proximity to the Confederate lines.  Captain James H. Wood, 4th New York Heavy Artillery, commanded the six mortars assigned to the Second Corps.  Wood wrote:

At 12 m. 3d of June one section (two pieces)was first placed in position at Cold Harbor, at a distance of about 800 yards from the rebel lines. The charge of powder used was 6 ounces and the length of fuse 15 seconds. The mortars were stationed in a hollow in rear of a belt of woods; 80 rounds were fired. It was reported by the front line of battle and the skirmishers of the Union forces that the shells made great havoc with the enemy, nearly every one exploding in their midst. At 7 p.m., by suggestion of General Barlow, the entire battery withdrew to the rear.

But the mortars would return.  That night the Federals completed mortar positions just 150 yards from the Confederate lines.  When the morning broke with heavy musketry, the mortars were ready:

At this place the charge of powder was 2 ½ ounces and the length of fuse 7 ½ and 8 seconds. The effect was excellent, and in about half an hour the rebels ceased to fire entirely. The position was such that the damage caused by the explosion of the shells was plainly discernible; and it was reported furthermore by our skirmishers that great execution ensued and the utmost consternation was visible among the enemy. The battery was highly complimented by Major-General Barlow and Brigadier-General Owen.

But their work soon attracted Confederate attention. Confederate field artillery fired in an attempt to damage or destroy the mortar battery.  But being so low and behind works, this did little good.  Confederate sharpshooters were more effective, preventing the gunners from standing up to aim or manage the mortars.  As a counter, the mortars began firing on the sharpshooters:

It was determined to try the effect of the mortar shells upon them and the whole battery delivered its fire, with the same charge of powder and length of fuse as at first. The result was almost instantaneous. Their firing was suppressed and was not resumed for several hours. It is perhaps not improper to observe that, during this affair, 2 rebels were seen to be blown 10 feet into the air, with heads detached. Their companions wildly scattered in every direction, and our infantry (General Owen’s brigade) giving a cheer, delivered a volley with telling effect.

Afterward the Confederates treated the mortars with caution.  Wood observed, “… that the enemy had fallen back in front of the mortars, leaving but a few skirmishers and sharpshooters in their front line of breast-works.”  In effect, the mortars had created a zone in which the Confederates could not operate.  While not a large zone, at least that offered some tactical advantage to the Federals.  But the Federals would need many more Coehorns if this was to be a useful advantage.

On the other side of the lines, the Confederates likewise started looking to vertical fires.  At that time, the Army of Northern Virginia lacked Coehorns.  But, Brigadier-General William N. Pendleton noted in his report on the campaign one adaptation of field artillery to the need.  “A 24-pounder howitzer of McIntosh’s battalion was adjusted a little in rear of the line and served as a mortar. It did good service in annoying the enemy’s working parties.”

Soon the howitzer and the Federal mortar began exchanging fires, as Wood recorded:

… the rebels fired at our forces with good range, using what was supposed to be a 24-pounder howitzer, trained as a mortar. The projectile thrown was spherical case-shot, by the explosion of one of which a man and a mortar were struck, but no serious damage was done to either. A new supply of ammunition having been received, it was decided to silence the rebel machine, if possible. By observing the smoke of their discharges, it was estimated that the distance was about 800 yards. A charge of 6 ounces of powder and a 15-second fuse were used, and after about one dozen discharges the enemy’s machine was silenced.

Wood’s mortars continued to do good work during the fighting at Cold Harbor.  The gunners had become very well practiced in the art of laying shells where needed.  Later, the mortars engaged in some more counter-battery fire, with good results:

On the 11th the remaining section, in charge of Captain Jones and Lieutenant Moore, was employed in firing at a rebel battery of light 12-pounders, which had opened upon a Union battery a short distance to our left. The mortars were estimated to be about 800 yards from the rebel battery. The charge was 5 ½ ounces and the length of fuse 15 seconds. The first shot struck on the left of the battery on a sand-bag breast-work, tearing a large hole therein. Another exploded inside the parapet, another in rear of the battery, another a short distance to the right. Assisted by the Union battery (light 12-pounders), the enemy’s guns were silenced. After this a few shells were thrown into a house almost in front of the mortars and 300 yards distant. The charge was 3 ½ ounces and the fuse 10 seconds in length. The house was a refuge for sharpshooters. One shell broke through the roof and exploded in the house. No more shots were observed to come from that locality.

With both armies remaining in close proximity for more than a week, the mortars were an idea weapon to use.  But there were precious few of them at the front.  Back in Massachusetts, Ames Manufacturing had a batch of fifty of the little mortars ready for inspection.  More Coehorns were on the way.

(Citations from OR, Series I, Volume 36, Part I, Serial 67, pages 527-8, 1050.)