Leveling, Pointing, and Elevating Field Guns

Emerging Revolutionary War welcomes back guest historian Karl G. Elsea

If you want to know the process of how field guns were fired in a battle such as Trenton or Monmouth, watching the National Park Service or re-enactors fire a cannon, you will only get part of the story. Important parts of the procedure are almost always missing. Here is a more complete presentation of the process; and, how leveling, pointing (aiming), and elevating a field gun were performed.

Major William Congreve said it best in his instructional training works at the Royal Military Repository in the late 1700’s: “It is of the utmost Consequence to the Service to fire so as to do Execution, for Shot flying over the Enemies head only hardens them and discourages your own Troops.” “Rounds must never be fired with-out pointing the Gun carefully each time and paying great attention to the Elevation.”[i]

After the commands, unlimber piece (un-attach the gun from the limber), take off apron (remove the vent cover), take out tompion (remove the “plug” at the muzzle of the gun), the gunners would perform the following activity with-out a specific command. This was a critical function and is not usually shown when firing a gun. It was to level the piece. As stated in their training, “and which ever Wheel stands too high, the Earth must be loosened in the rear, and the Gun drawn gently back until the Bubble rest in the Center of the Tube.”[ii] The science was simple, the trunnions on the barrel must be level or the barrel will move in a non-vertical plane and thus be off target. Leveling the gun was of great importance. The Artillerist’s Companion 1778 states it was an artillerist’s function, “Quadrating a piece [barrel] mounted, is to see whether it be directly placed, and equally poised in the carriage, which may be found by a gunner’s instrument called a level or perpendicular.”[iii]

The following picture shows what was called the Gunner’s level or the Spirit Level. It was the quintessential instrument carried by gunners to level the gun. In a cylinder in the middle of the gunner’s level was a vial and when the trunnions are level the bubble in the vial will be in the middle. At that point the gun was leveled.

(Author’s Level and Photograph)

The next activity was sometimes required to point the gun and it also required the Gunner’s Level. The level could be used to place a noticeable mark indicating the top of the base ring and the top of the muzzle ring. These two marks constitute what was called the “centre” [center] line of the cannon. The activity of marking the “centre” line was performed immediately after leveling the cannon unless the points or the line were already marked on the cannon. This line on the barrel was called the “gun metal line.” On many of the guns of the period the metal line marks were discretely engraved into the design on the barrel. For example, on this patriot cast Byers’ gun the base ring line, touch hole, and liberty pole mark one end of the “gun metal line.”

After these tasks (leveling and marking) were complete the gun was ready for pointing (aiming).  With regards to the Patriot’s drill, there was a distinct difference between the primary source drills of William Stevens and Louis de Tousard. Stevens records that “Take Aim” happens after the command “Prime.”[iv] In Tousard’s drill “Take Aim” takes place before “Prime.”[v] There was a reason for these differences, and it depended on how the gun was primed. The use of a priming tube, whether tin, reed, or quill, could potentially block the sighting line. Tousard’s drill avoided this problem by sighting before the priming tube was inserted. It should be noted the centre line passed over the touch hole. It was noteworthy that the British drill specifically mentions pointing before the tube was inserted into the touch hole. The British drills for a six-pounder stated, “The man who serves the Vent … not put the tube in until the Gun is pointed.”[vi] With regards to Steven’s drill, the priming likely consisted of using powder to touch off the charge, thus the “take aim” command could take place after priming. Using powder only to prime did not block the sighting line. Tousard’s drill assumed tubes were used in priming. British and Patriots used tubes as the preferred manor in priming field guns.

(Author’s Photograph)

Last came the task of elevating the gun barrel. The need for proper elevation of the barrel was demonstrated by noting the psychological impact of cannon fire as shown in the following contemporary quote, “it having been often proved that Soldiers have been more alarmed and put in confusion, by seeing Shot hopping to them, than by having double the Number of their Comrades killed by their sides without seeing it.”[vii] That quote showed the importance for shot to land and bounce somewhat in front of the soldiers. Elevation was adjusted to accomplish that task.

For elevation the gunners would know their individual piece and the characteristics concerning how the various types of shot with varying powder charges would fall. The Officers would likely have some recordation measuring the needed elevation for the distance to first graze. First graze was the range at which the shot would first touch the ground. That recordation would allow the gunners to know what elevation to use for their barrel.

The gunners would also know what the dispart (half the difference between the diameter of the base ring and muzzle ring) was for their individual gun. Dispart was the key to understanding that aiming the gun on the centre line automatically elevates the barrel. Dispart could be quickly measured in the field by placing the vent pick into the touch hole until it reached the bottom, and then subtract that measurement taken at the muzzle from the bottom of the tube to the top of the muzzle ring. As noted above, when the cannon was aimed using the centre line (“gun metal line”) then the resulting cannon ball strike on level ground was called the “Common range.”  Common range was different from “point blank range” which was the distance when a cannon ball first touches ground when fired from a level barrel on level ground.

There was an exception to aiming and elevating the gun. The exception was if a gun were to be overrun. British training materials stated, “Case Shot may be fired as quick as the Dragropemen can draw the Gun up to its proper Position in the Interval again, which will allow the Non Commissioned Officer a sufficient time to direct the Gun nearly to the Center of the Enemies Battalion and give a pretty good guess at the Elevation.”[viii]

[i] Adrian B. Caruana, The Light 6-Pdr. Battalion Gun of 1776, (Alexandria Bay, NY: Museum Restoration Service, 1993), 27.

[ii] Caruana,33.

[iii] T. Fortune, The Artillerist’s Companion 1778, (London: Whitehall, 1993), (Alexandria Bay, NY: Museum Restoration Service, 1992), 9.

[iv] William Stevens, A System for the Discipline of the Artillery of the United States of America, (New York: William A. Davis, 1797), 68.

[v] Louis de Tousard, Artillerist’s Companion on Elements of Artillery, (Philadelphia: C and A Conrad and Co., 1809), 140-141.

[vi] Adrian B. Caruana, The Light 6-Pdr. Battalion Gun of 1776, (Alexandria Bay, NY: Museum Restoration Service, 1993), 29.

[vii] Caruana, 27.

[viii] Caruana, 27.

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