Mortars and shells wanted at the front: Importance of vertical fires at Petersburg

We often read the Petersburg siege demonstrated the emergence of “modern war” in some fashion.  The “coffee table book” history draws the the comparison between Virginia trenches of 1864-5 to French trenches of 1915-8.  There is some resemblance, but no more than any functional nature would derive.  Men can only dig a hole in the ground for protection in a finite number of combinations.  Nice surface comparison, but for the most part the trenches are not exactly a mountain of evidence for the “modern war” argument.

If looking to draw positive connections between Petersburg and the tactical nature of warfare in 1915-18, there are two aspects I suggest we examine – the increased use of vertical fires and  changed operational tempo.  That latter point – what we call OPTEMPO in modern parlance – I’ll save for a later post.  But I have mentioned vertical fires earlier this year in relation to the Overland Campaign… particularly Cold Harbor.  And of course, mortars were heavily employed to support the assault after the mine went off.  In the late summer of 1864, the mortars took on added importance at Petersburg. A series of correspondence on August 14, 1864 demonstrates this. That morning, Brigadier-General Henry Hunt wrote to his capable subordinate, Colonel Henry L. Abbot in charge of the siege artillery, directing mortars to the front:

Four 10-inch mortars with a proper supply of ammunition are wanted in the battery near the Taylor house to control a battery of 32-pounder rifles just beyond the crest, distance from 1,200 to 1,500 yards. It would be well to get them out to-day ready to move; they may be ordered into battery to-night. I will inform you then whether to send them. Please answer.

Hunt’s request was to meet a specific tactical need – silencing a Confederate battery that occupied a particularly troublesome position.  The answer to this problem was not direct, or horizontal fire.  Rather he proposed using heavy mortars to fire indirectly, or vertically, onto the Confederate position.  Abbot answered almost immediately that morning and set in motion actions to place the mortars that night. Abbot later suggested a specific position for the mortars, based on earlier experience along that line:

If the 10-inch mortars are ordered forward, I would earnestly request that they be put in the fourteen-gun battery where Pratt’s 4½-inch guns were. The range is essentially the same. The approach to this battery is very good, and to the old battery very bad, a matter of great importance in supplying 10-inch ammunition on account of its great weight; and, moreover, this battery is well made and the old battery very ill constructed, constantly caving under mortar fire.

Looking back at Hunt’s map illustrating the artillery support during the Battle of the Crater, Pratt’s battery is indicated by the number “24” and circled in blue below:


The correspondence does not specify which Confederate battery was the target.  For the map above, I’ve highlighted one such battery, which would be “beyond the crest” and approximately 1,500 yards distant.  Notice the close proximity to the mine crater. The range cited was well within the capabilities of field pieces. The Confederate guns mentioned were indeed large caliber weapons.  But the Federals might have concentrated the fires of several batteries to damage the battery.  However, having read about the thousands of shells dumped on Fort Sumter, we must ask how long and at what cost would that be completed?

There is no mention if Hunt required the use of 10-inch case shot from the mortars, as used during the Battle of the Crater.  That particular projectile, of experimental nature, would have done well to silence the Confederate battery while field pieces demolished the earthworks protecting the guns with direct fire.

Concurrent with the correspondence with Hunt, Abbot also opened a request for more mortar ammunition… and not just a routine request… to Captain Theodore Edson, Ordnance Officer at Fort Monroe:

I am out of my supply of Coehorn mortar shells and the rebels are taking advantage of it. Please send me any shells and wooden plugs which you can possibly procure, on the mail boat, telegraphing me when they start. I don’t care for prepared ammunition. Time is very important.

Backig this up, Abbot further explained the pressing need for mortar ammunition to Brigadier-General George Ramsay, Army Chief of Ordnance in Washington and indicted this was a long standing request:

I have sixteen Coehorn mortars in position and not a shell in depot for them. The rebels keep up a constant mortar fire on us. I don’t care for prepared ammunition; all I want are shells, fuse-plugs, and paper fuses. These must be received very shortly or the army will suffer. I wrote on 15th ultimo, and telegraphed on 19th ultimo and 11th instant for a large supply. Please inform me at once whether I am to be supplied. Please also send 2,000 Parrott time-fuse plugs for siege guns.

The Confederates had also learned the value of vertical fire, and were now in position to employ some of the heavy mortars from Richmond along with some expedient weapons.  And at the same time, the Confederates were commencing production of their own Coehorn mortars.

Fast forward to 1917. When preparing the American Expeditionary Force for combat in France, American officers found themselves short of artillery in general.  But most acutely they called for howitzers and mortars capable of high angle fires.  Henry Abbot would have given them an “I told you!” look.  Vertical fires would become the dominant form of artillery support on the battlefield.

(Citations from OR, Series I, Volume 42, Part II, Serial 88, pages 182-3.)

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.)


“The Coehorn mortars were employed wherever circumstances would permit”: Mortars at Spotsylvania

When the Army of the Potomac broke winter quarters in early May 1864, the Artillery Reserve brought along a somewhat novel weapon – 24-pdr Coehorn mortars.

Seven Days 26 May 12 170

Eight of these mortars, with 100 shells each, traveled with the reserve park, manned by Company E, 15th New York Heavy Artillery.  Of their performance and utilization, Brigadier-General Henry Hunt provided a single sentence in a section of his report on the Battle of Spotsylvania Court House:  “From the 8th to the 16th the Coehorn mortars were employed wherever circumstances would permit of their use, and always with good results…”  The results were so good, in fact, that by June, every corps in the army received their own allotment of Coehorns.

As I mentioned in an earlier post, Hunt saw these light mortars as a means to provide fire support in a particular niche not served by the normal field guns (and for which he did not think howitzers could provide).  Recall the Coehorns had provided remarkable support during the siege on Morris Island the previous summer.  And were requested, but not provided, for the siege at Vicksburg – where ersatz wooden mortars filled in.

That niche, defined, was to lay explosive projectiles on a position shielded from direct line of sight, and thus fire.  Such a tactical requirement was seldom of great importance in a pitch battle, with maneuvering forces.  But where the armies sat in close proximity for days on end, and fortifications grew up to protect those forces, the mortar’s high angle fire was of great importance.  So 150 years ago today, with the armies tangled in a series of entrenchments in Spotsylvania County, those eight Coehorns were arguably more useful than a couple batteries of 3-inch rifles.

There was one other suggestion for vertical fire made by Hunt prior to the campaign which might rank as novel… or perhaps even bizarre.  I’ll take a look at that in a later post.  But as a teaser, think a “gun-howitzer-mortar.”

(Citation from OR, Series I, Volume 36, Part I, Serial 67, page 286.)