“Light 12-pounders to be used as mortars”: A Spotsylvania ‘what if?’ from the artillery persepctive

I’m a bit behind on “coverage” of artillery subject on my planned sesquicentennial-themed time line.  So I hope you readers will indulge as I back-track here (and a few more times over the next few weeks), chronologically speaking.  The letter below properly fit into a post for the first week of May when I referred to the Army of the Potomac marching out of the Winter Encampment.  Among the last letters Brigadier-General Henry Hunt sent from his headquarters near Brandy Station was this message to Colonel Henry Abbot, 1st Connecticut Heavy Artillery and designated commander of the siege trains:

Artillery Headquarters, Army of the Potomac,
May 4, 1864.
Colonel Abbot:

My Dear Colonel: I have received your note of the 1st instant, and am glad to see things are progressing so favorably. I see you have as yet no Coehorns shipped, and that reminds me to ask you how many Coehorn mortars can be got. We will probably need all we can get. I have eight with me, and it would be well for the Ordnance Department to collect all they can. We move to-morrow; so you will soon hear from us in some shape, and will know about how soon the siege train will be required. Address as usual.
Truly, yours,
Henry J. Hunt,
Brigadier-General.

Aside from the “My Dear Colonel,” this message doesn’t raise many eyebrows.  Though it is important to note that even on May 4, before a single shot was fired in the Overland Campaign, Hunt recognized the need for Coehorn mortars.  And he wanted a lot more than eight.  But we knew that already.

More interesting to us artillery-types is the postscript:

P. S.–Would it not be well for you to set apart a few men, with a good officer with some experimental practice with light 12-pounders to be used as mortars, i.e., try the ranges with different weights of powder, and see how the carriage will stand it, if necessary, to throw very heavy showers of shell in curved fire? I think that by digging a hole, and so lowering the trail–diminishing the charge–we will, at a pinch, be able to turn our light 12-pounders to very good account. Provision should be made, if the experiments prove satisfactory, to send on short notice a supply of 12-pounder shell. Can you send me, with your next letter to headquarters Army of the Potomac, a table of ranges for heavy rifled guns–30-pounder Parrotts and 4½ inch? I have none, and would like to have them about me; also a copy of heavy artillery.
Yours, truly,
H.

Let me work this from the end back.  Hunt’s staff, having planned around the use of field pieces for the last year, now needed a refresher on heavy and siege weapons.  Hence the need for range tables for those heavy guns.

But the really interesting section is the request for trials using Napoleons as mortars.  For those less acquainted with Civil War artillery, the standard carriages used during the war allowed a dozen degrees of elevation, give or take depending on the gun and carriage.  For true vertical fires, the weapon must have at minimum 45º elevation.  The only way to achieve such elevation for a Civil War field gun on a standard carriage was, as Hunt suggested, to put the trail in a hole.  And since with the trail in such arrangement, the gun could not recoil, the firing charge had to be reduced lest the force destroy the carriage.

You might ask, what advantage might be gained by firing at such high angles?  A tactical advantage.  With more elaborate field fortifications appearing on the battlefield, the horizontal fires of conventional field guns, and even to an extent howitzers, was at a disadvantage.  Both sides built up heavy front works – higher parapets made of heaped earth and logs.  The penetrating power of direct fire artillery – even the rifles – was not sufficient to break such barriers without a prolonged bombardment.  But vertical fire,  such as from a mortar, could place a shell beyond those works, and do great damage to the defenders.

So how did those trials go?  Three days later Abbot sent this update:

Fort Richardson, VA., May 7, 1864.
Brig. Gen. H. J. Hunt,
Chief of Artillery, Army of the Potomac:

General: Yours of 4th instant is received. There are only five Coehorns now at arsenal, but the rest are expected very soon, and fifty have been ordered with all possible speed. I have ordered experiments with the light 12-pounder gun as a mortar to-day, and will report results as soon as obtained. The Ordnance Department has an abundant supply of ammunition for them on hand. I send by this mail a copy of heavy artillery, which contains an addition to the old range table prepared by General Barry, giving the best rifle ranges known to me; also a similar table prepared by Captain Treadwell, Ordnance Department. I inclose a table of experiments on the new-model 10-inch mortar, to show the difference between the Gomer and elliptical chamber; also a copy of a report of some experiments with spherical case from a 10-inch mortar, which are so successful that I have ordered a large supply of 12-pounder spherical case balls for our train. I also think of taking two 12-pounder Whitworths along. They make elegant sharpshooting to dismount guns. They are very light, and may be of service for such special uses. The following is the present condition of my train afloat: 4½-inch–18 guns. 20 carriages, 20 implements, 20 platforms, 6,520 rounds; 30-pounders–10 guns, 20 carriages, 10 implements, 20 platforms, 5,025 rounds; 10-inch mortars–10 guns, 10 carriages, 10 implements, 10 platforms, 2,000 projectiles; 8-inch mortars–20 guns, 9 carriages, 20 implements, 2,600 projectiles; 8-inch siege howitzers–10 guns, 4 carriages; Coehorns–3,796 projectiles; 100-pounders–6 guns, 6 carriages, 1,400 projectiles; 1,250 barrels powder, 1 battery wagon, 1 forge, 4 sling carts.

Very respectfully, your obedient servant,
Henry L. Abbot,  Colonel First Connecticut Artillery.

Only five more Coehorns?  I should mention Brigadier-General Albion P. Howe’s report on the Washington Defenses from May 17 tallied over twenty Coehorns in the forts.  As indicated in Abbot’s letter, the desired range tables and a lot more information went forward to Hunt.  (Two other interesting topics here – the 12-pdr Whitworths and the 10-inch mortar case shot – I will save for later posts.  The latter becomes important at Petersburg, particularly in the Battle of the Crater.)

But he had not gotten around to trials of the Napoleons as mortars.  Nor would he.  Two days later Abbot received orders to move his force to the Bermuda Hundred and join Major-General Benjamin Butler’s force.  At that point, Abbot’s attention was to operations at the front and not ordnance experiments. UPDATE:  Abbot wasn’t able to test, but his subordinates were.  See this post.

However, consider this “what if?”  Going into the Overland Campaign, the Army of the Potomac had over 100 Napoleon guns.  What if the requested experiments had gone on earlier in the winter, with a proper and refined employment method, to include range tables, been derived?

Now… what if the assault on the Bloody Angle has been initiated by 25 or 50 or even 100 Napoleons firing shells at high angles into the Confederate works, instead of just eight Coehorns?  Granted, as the employment of the Coehors on May 12, 1864 demonstrated, poor accuracy of vertical fires in the black powder era argued against its use in close proximity to friendly forces.  But a preparatory bombardment to open the way for an infantry assault was possible. Similar bombardments supported assaults on entrenchments over fifty years later during World War I.  And for good measure, unlike 1917′s trenches, the Confederates at Spotsylvania had no prepared overhead cover.

(Citations from OR, Series I, Volume 36, Part II, Serial 68, pages 373, 484-5.)

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3 responses to ““Light 12-pounders to be used as mortars”: A Spotsylvania ‘what if?’ from the artillery persepctive

  1. John Wells, 3rd US Artillery, N-SSA

    Craig, I have a vague recollection of reading in some period artillery manual or other that the Napoleon could be reversed on its carriage to allow high angle of fire “mortar practice” The carriage would then have the trail elevated and support placed under the cascabel could control elevation angle. Surprisingly light charges will loft a 12-pounder ball great distances, even with coehorn-length tubes, so a light gun-howitzer would really be able to “sneeze” them out there! Have you found anything to substantiate this, or did I dream it?? John W.

    • I don’t know about the Napoleons. I do know the 8-inch siege howitzers carriages were designed for such. However, I’d like to see some range tables for such use. Would be interesting to compare with 8-inch mortars.

  2. Pingback: Napoleons (and siege howitzers) as mortars: More data and range tables! | To the Sound of the Guns

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