Light gun for inshore duties – 12-pdr, or 3.4-inch, Dahlgren Rifled Boat Howitzer

On September 15, 1864, Brigadier-General Rufus Saxton made a request for naval support to help picket the backwaters behind Morris and Folly Islands:

I have the honor very respectfully to request that, if consistent with the interest of the service, a navy launch, manned and armed with a rifled 12-pounder howitzer, may be placed on picket service in the creeks opposite Long Island and in Stono and Folly Rivers.  Such a boat will be of very great service there.

Although the Army’s forces had long patrolled and picketed the marshes in that sector, recent reductions in the force left them short of personnel.  Shifting light artillery to other sectors (such as guarding the 600 Confederate prisoners) meant the Army had few field pieces –  which were unsuited for duty in the marshes to begin with.  Aside from the little mountain howitzers, the Army’s system of artillery lacked anything light enough for handy operation in the boats used in the backwaters and bays.

The 12-pdr rifled howitzers were used often around Charleston during the war.  I’m of the mind these weapons were valued due to greater accuracy at long range when compared to the smoothbore howitzers.  Let me reach back to some charts posted several years back to demonstrate the characteristics of these rifled boat howitzers.  First comparing the different types of Dahlgren Boat Howitzers:

The Navy introduced the 12-pdr rifle (next to last column on the right) in 1861.  The rifle used the same bronze casting as the 12-pdr Heavy Boat Howitzer (second column from the left), but with a 3.4-inch rifled bore.  Early rifles had three groove rifling.  That was later increased to 12 grooves.  The smaller bore diameter translated to a slight increase in weight of the weapon to 870 pounds.  That meant the rifle was slightly heavier than a standard Army 12-pdr field howitzer.  But because the rifle used the Dahlgren carriage, overall weight remained lower than the Army type in action.

The 12-pdr rifle fired shot, shell, and case shot (shrapnel).  The Navy Ordnance Instructions of 1866 credit the 12-pdr rifle with a range of 1,770 yards at 5º elevation using a 1 pound powder charge (time of flight was 6 seconds).    That compared to 1,085 yards for the same powder charge and elevation for the smoothbore 12-pdr Heavy Boat Howitzer.

During the Civil War, the Navy received 423 of these 12-pdr Rifled Boat Howitzers.  The rifles saw frequent use during the war, particularly around Charleston.  Aside from the Army’s request, the 12-pdr rifles were used from the decks of the monitors to fire upon grounded blockade runners.

Having established the weapon’s importance at this time 150 years ago, let me turn to a pair of the fifteen survivors for a walk-around.  Two 12-pdr Rifled Boat Howitzers are on display today at Battery Jameson, part of Fort Lincoln, in Brentwood, Maryland… allowing me to bridge wartime activities at Charleston back to Washington, by way of John Dahlgren and the Washington Navy Yard!

Bladensburg 110

The two howitzers are registry numbers 211 and 250, both produced by the Navy at the Washington Navy Yard.  (Ames Manufacturing also produced 26 of this type in 1862.) From a distance, the rifles have the same appearance as the 12-pdr heavy smoothbores:

Bladensburg 122

Notice the location of the fixtures, particularly the lock-piece mount, rear sight base, and pierced knob.  Again much the same as with the smoothbore gun:

Bladensburg 111

The measure of axis for the lock-piece was the same as on the smoothbore:

Bladensburg 116

Looking at the muzzle, we see the difference with the rifle:

Bladensburg 121

Yes, 12-groove rifling:

Bladensburg 119

The rifle retained the front sight base.

Bladensburg 114

Markings on the barrel also give away the type:

Bladensburg 113

In this case – Rifled 12 pdr // Boat Howitzer // 1863 // J.A.D.  The later being Rear-Admiral John Dahlgren’s initials.  There are other markings on these howitzers, and some are rather interesting in regard to the “administrative” history of the guns.  But due to the years of exposure, many have been obliterated.

There are some interesting variations among surviving 12-pdr rifled boat howitzers.  Some were bored out from rifles to be standard 12-pdr smoothbore weapons.  The assumption is the Navy learned, as did the Army, that bronze was not good for rifled guns.  There are a few of the steel versions around, which I’ll show in a walk-around at a later date.  At least one 3-groove rifling version has survived.  At least one was converted to brechloading, either for experiments or as a saluting piece.  Also there were several steel guns cast by Norman Wiard.  Those should not be confused with Wiard’s “puddled wrought iron” rifles of the same caliber produced for the Army’s “Marine Artillery” and used in North Carolina.

Dahlgren’s 12-pdr Rifled Boat Howitzer was mentioned on several occasions in correspondence and reports.  All indications are the weapon served its purpose well.  But as with all bronze pieces of the era, it was eventually rendered obsolete with the arrival of steel breechloading weapons.

(Citation from OR, Series I, Volume 35, Part II, Serial 66, page 289.)

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