Boat Howitzer
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Boat howitzers were an American Civil War artillery piece originally designed to serve aboard launches, but also saw extensive use on all types of Navy ships as well as on shore. Invented by John A. Dahlgren, his 12-pounder Boat Howitzers were considered the "best boat guns in the world."
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[edit] Carriage
Sometimes referred to as "go anywhere" howitzers, they are designed foremost for mobility. The pieces originally were supplied with two carriages, a field carriage, used both ashore and on deck aboard monitors and frigates; and a boat carriage for service in launches. The field carriage was built of forged iron to make it lighter, with either wooden or iron wheels. This made a medium/heavy 12-pdr weigh-in around 1200lbs, whereas a 12pd Napoleon field piece tipped the scales at over 2300lbs.
A trail wheel was located at the rear of the boat howitzer which, together with its light carriage, made the piece extremely mobile. A pin securing the trailwheel could be removed and the wheel pivoted upward for firing in order to limit recoil.
The guns had no limbers. Ammunition was carried in two boxes that would be transported on racks fixed to the carriage. Further ammunition was carried by the gun crew themselves. A full crew consisted of an officer and 16 men, each carrying 1 extra round in a leather or canvas haversack. Altogether a gun could expect to have at its disposal 72 rounds of ammunition before having to be resupplied. A trained gun crew could fire up to 8 rounds per minute in combat, but did so by omitting some steps in the loading process; this was seldom done in regular practice. This fact brought John Dahlgren to mention in his manual on the piece that a howitzer should fire no more than 1 round per minute, in order to save ammunition. The howitzer was moved about by hand, or prolonged, by means of a drag line attached to the trail of the piece. Because of this, their design limited their range of deployment, sometimes noted as less than 15 miles from a landing site.
[edit] Barrel
The barrel was fixed to the carriage with a loop forged under the barrel (similar to that found on carronades). A socket for the loop was provided on the carriage where a "lightning bolt" was inserted to join the two. This is as opposed to the trunnions found on field pieces. The gun was precisely balanced on over the loop, allowing easy removal from the carriage by simply removing the lightning bolt and applying a little weight on the muzzle of the barrel. Once the barrel was tipped down where its muzzle rested on the deck, the loop would slide out of the socket and the barrel would stand upright on its muzzle.
Boat Howitzers were forged out of either bronze or iron, though bronze pieces were much more abundant in their 12-pounder models. 20-pdr and 24-pdrs. were made as well, with their service mainly restricted to shipboard. Smoothbores dominated, though rifled steel barrels were designed as well. The 12-pdrs came in two models, a light, with a barrel of approximately 350 lbs., and a medium (later referred to as "heavy") 12-pdr with a barrel weighing in around 730 lbs.
[edit] Firing
The medium had a maximum range of 1,085 yards with shell (projectile) or 1,150 yards with shrapnel propelled by a 1-lb. powder charge. Boat howitzers were not intended to fire solid shot; ordnance was restricted to grape, canister, shell, and shrapnel. Dahlgren noted that heavier charges could be withstood by the barrel and therefore longer ranges achieved, however, the strength of the carriage could not sustain the shock and recoil from such a charge being discharged. Durability was sacrificed for mobility.
In firing, the Boat Howitzer used a modified Navy Lock and pan head primer. A lanyard was threaded through the lock in such a way that a pull on it would allow the hammer to fall on the primer. The lanyard was pulled until the hammer fell, never yanked. A vent hole was designed into the lock mechanism to allow the escape of gases. Friction primers could be used as well instead of the pan-head primer and lock.
[edit] Service
Their design was for amphibious operations: the guns would go ashore on their sea carriages in the launch for a frigate, with the land carriage stored in the stern sheets. A boat carriage was positioned on the bow to accept the barrel of the howitzer, whereas the launch could serve as a gunboat. Once hitting the beach, the land carriage was unloaded, the barrel of the boat howitzer removed and placed upon it.
Boat howitzers would see service aboard numerous frigates and monitors serving in the blockade and on western rivers. On both they would sit on the field carriages on the decks of the ships. In an interesting note, on the iron decks of monitors, cloth or rope was sometimes lashed to the iron treads of the wheels to limit the noise as they moved along the deck. This was especially useful when navigating a western river, with possible hostile forces on its banks that could use the clang-clang of a moving howitzer to home-in on a monitor upon the river. The was also done to again attempt to control the recoil.
Aside from use on naval launches, boat howitzers saw service ashore as well. At First Bull Run, two boat howitzers were manned by Company I of the 71st Regiment, NY National Guard. The unit had trained on boat howitzers while deployed at Washington D.C., and when called to Bull Run, brought two of them attached to I Company. The guns unfortunately had to be left behind during the unit's withdraw and were captured by Confederate forces.
During the Antietam campaign, the 9th NY Infantry (Hawkins' Zouaves), Company K (Whiting's Battery) employed 5 Dahlgren Boat Howitzers, and the Confederate unit of Grimes' Portsmouth Battery had 3 Boat Howitzers under its command.
The 1st Regiment, New York Marine Artillery also armed themselves with boat howitzers, using it for its designed use of amphibious expeditions. The unit participated in 16 raids along the North Carolina coast employing their boat howitzers.
