In the last post on the Dahlgren Boat Howitzers, I related the requirements and some of the design details of the type. In order to meet the tactical and operational demands of the intended mission, Dahlgren opted to design new carriages. Keep in mind there was not one, but rather two carriages for the new howitzers – one for mounting on boats and one for land use. If the recollections of Dahlgren’s widow are correct, the officer came up with the fundamental design for a carriage while sleepless one night, and proceeded to his office to layout what became a most successful model (Memoir of John A. Dalhgren, by Madeline Vinton Dahlgren, p. 133).
For use on boats, Dahlgren opted for a sled carriage somewhat similar to the carronades. The entire “sled” sat upon a bed which pivoted about the front of the boat to allow firing forward and to each side. A plate below the bed connected with the sled and provided resistance to control recoil. The illustration below shows two hand screws used to fix and tighten the plate to the sled.
In some regards, the sled-bed and pivot recalled that of the light gunades mounted on merchant ships. However, Dahlgren’s boat carriage dispensed with breeching ropes, partly due to a rather efficient design but due also in part to the light charges used. According to Dahlgren’s notes, a 12-pdr with service charge only recoiled 22 to 17-inches (Dahlgren, A system of Boat Armament, p. 30).
Dahlgren’s design included fixtures for standard ship’s boats. Three pivot plates, forming an equilateral triangle, provided anchor points for the front of the bed. Supporting the carriage and cannon was a set of wood braces added to the boat’s existing gunwales and cross beams, forming a “T” under the bed. With this arrangement, the crew would fix the bed to a pivot plate with a pin, then slide the bed along the braces for traverse. Elevation was corrected by the elevating screw running through the knob. These configurations allowed mounting of the cannon on the bow and/or stern. But when use ashore was required, a metal frame field carriage was carried on either the bow or stern.
Upon landing, the crew moved the field carriage forward (or aft as the case may be!) and positioned the axle just under the howitzer near the mounting loop. The crew would then pull the loop-bolt thereby disconnecting the howitzer from the sled, then man-handle the piece onto the field carriage. Once fixed to the field carriage, to include remounting the elevation screw, the weapon was run over the boat’s gunwales by use of drag-ropes. Dahlgren stated the entire transition could be accomplished within a two minutes – from the time of fire from the boat to the time of fire from the field carriage (Dahlgren, A System of Boat Armament, p. 85)
The field carriage, constructed of wrought iron, weighed under 500 pounds. The illustration above seems to show wooden wheels, but most surviving carriages have iron wheels. Aside from the two wheels on the axle, a trail wheel supported the weapon during transport. The trail wheel was turned up, allowing the carriage to rest on a skid, during firing. This all metal carriage used reinforcing rods from the trail to the axle for added strength. A dozen men pulled the howitzer using a drag rope, “…a force always disposable from any boat that could carry a gun of this class.” (Dahlgren, A System of Boat Armament, p. 33)
Dahlgren dismissed the use of a dedicated caisson for ammunition. Instead he opted to provide fittings to carry some rounds on the carriage and relying on the gun’s crew to carry additional rounds. In short, the reasoning was the landing crew was not a force intended to spend much time ashore without extended support arrangements anyway. If more ammunition was required, then more men would be allocated. And a dedicated caisson might consume space needed for more valuable resources. Navy ordnance instructions, as late as 1866, allocated two transporting boxes fixed to the axles with no mention of caissons (Ordnance Instructions for the United States Navy, p. 23). However, photographic evidence hints that the Navy used at least some caissons.
Dahlgren’s two carriages offered flexibility to the weapon system. Compact, light, and simple, both the boat and field carriages met the needs of boat howitzer’s varied missions. I would argue that the carriage system was the critical component in the system.
Next I will look at the variants of howitzers within the “family,” the ammunition used, and employment practices. And as time permits, perhaps discuss the wartime uses of these interesting pieces.
Aside from on site notes and links provided above, sources consulted for this post were:
Hazlett, James C., Edwin Olmstead, and M. Hume Parks. Field Artillery Weapons of the Civil War, Revised Edition. Urbana and Chicago: University of Illinois Press, 2004.
Olmstead, Edwin, Wayne E. Stark, and Spencer C. Tucker. The Big Guns: Civil War Siege, Seacoast and Naval Cannon. Alexandria Bay, NY: Museum Restoration Service, 1997.
Ripley, Warren. Artillery and Ammunition of the Civil War, 4th Edition. Charleston, S.C.: The Battery Press, 1984.
Tucker, Spencer. Arming the Fleet: U.S. Navy Ordnance in the Muzzle-Loading Era. Annapolis, Maryland: Naval Institute Press, 1989.