Iron Frogs: 8-inch Model 1861 Siege Mortars

Once again, let me return to one of the photos from Broadway Landing:

This time, let me call attention to the squat mortar in front of the row of howitzers:

Like an iron frog, just sitting quietly.  Waiting for a chance to grab a passing fly.

It is/was an 8-inch Siege Mortar, Model 1861, made to the new pattern established by the Ordnance Board the year before.  So first let’s compare the Model 1861 to the previous production types discussed earlier as the Model 1840.

With the addition of 85 pounds in weight, the Model 1861 added a bit of length to the bore.  The weight and design also allowed for a small increase in powder charge.  This allowed for a modest increase in range, according to the firing tables.  But those statistics cover up several improvements, best described through the “walk around.”

Perhaps the most important statistic in the chart is the number produced – over four times the number of Model 1840.  Remarkably more than half, at present count nearly 90, of those produced survive today.  And the survivors offer plenty of opportunity for detailed, up-close examinations… and discussion of those improvements.

As the chart indicates, three vendors produced the 8-inch Model 1861.  The first to commence deliveries was Cyrus Alger of Boston.  Thomas J. Rodman inspected the first, credited in April 1862, of a batch of ten.  Rodman also inspected the second batch of 17 delivered between October 1863 and February 1864.  There’s another Rodman connection beyond the inspection stamps.  The second batch (and possibly subsequent castings) used the Rodman method of hollow casting.  Later Alger delivered twenty more, bringing their total to 47, which were inspected by other officers.

Fort Pitt Foundry commenced production of the type in late 1862 with initial deliveries in January 1863.  As with Alger, contract specifications for those cast in 1863 called for hollow casting.  Fort Pitt delivered its last of the type in September 1864, completing a 73 example run.  I mentioned one of those Fort Pitt mortar in an earlier post about the guns displayed at Sunbury, Pennsylvania.

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8-inch Siege Mortar Model 1861 at Sunbury, PA – Fort Pitt

Muzzle markings offer details of the weapon’s manufacture:

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Muzzle of Fort Pitt #24

This mortar is registry number 24 from Fort Pitt.  It was accepted by Robert Henry Kirkwood Whiteley (R.H.K.W.) in 1864, weighing 978 pounds.  On the other side of the display is the next weapon produced in the registry sequence – number 25.

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Muzzle of Fort Pitt #25

Notice the raised numbers above the right trunnion on these mortars.

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Fort Pitt #25

The raised numbers were the foundry number, a unique practice used by Fort Pitt.  This number was often repeated on the right rimbase, in accordance with regulations.

And speaking of the trunnions, compared to the previous model, the trunnions in this year model moved from behind the chamber to the center of balance.  This was due to the use of a zero-preponderance elevation system, somewhat similar in concept to that used on the larger seacoast guns and mortars.  The mortars had a raised strip with rectangular sockets.  This allowed the use of an elevating bar, again just as with the big Rodman guns.  There was some deviation in the number of sockets.  Early Alger production 8-inch Model 1861 had three sockets.  Later they increased the number to eight.  Fort Pitt mortars had three.

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Top profile of Fort Pitt #25

There was some variation in the trunnion length also.  Alger production batches had trunnions 3.25 inches long.  Early Fort Pitt production had trunnions barely over 2 ⅓ inches.  The foundry increased the length to three inches and then up to the full 3.25 inches as production continued.  Those at Sunbury are behind an iron fence, but appear to be 3 inches long.

Notice also the lifting lug on top of the mortar.  This was yet another addition to the 1861 design.

Seyfert, McManus & Company, working from the Scott Foundry in Reading, Pennsylvania, produced 50 examples starting in August 1864.  All of their production came under a contract calling for hollow casting.  Two of those sit today in a cemetery in Lewisburg, Pennsylvania.

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Mortars and Memorial at Lewisburg

These are registry numbers 33 and 49, both accepted in 1865.  The mortars from Reading featured nine sockets on their breech.

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Breech of Seyfert, McManus mortar

Seyfert, McManus & Company mortars used the full 3.25 inch long trunnions.  Notice the absence of the lifting lug in this view.  These are mounted inverted and the lifting lug is underneath now.

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Lug on Inverted Mortar

Such prevents easy view of the vents.  The Model 1861 design called for two vents – one on the left initially drilled through and on the right with the last inch undrilled.  The mortars’ vents were not bouched.  When the left vent wore open with use, the artificer closed it with zinc.  He then drilled out the last inch of the right vent to put the weapon back in service.

The 8-inch Model 1861 Siege Mortar entered service as the “light” weapon in the family.  Wartime photos indicate that, in addition to work on the Richmond-Petersburg lines, the mortars saw service in the Washington defenses. Long after the war these weapons remained in depots as part of the Army’s siege train.  John C. Tidball included a section detailing the service of an 8-inch siege mortar in his 1884 Manual of Heavy Artillery Service.

Yet outside the intense period of 1864-65, the 170 8-inch Model 1861 Siege Mortars spent much of their time idle.  Perhaps, due to that long, uneventful service life, there are many of these “iron frogs” surviving as gate guards and memorials.

Next up, the 10-inch Model 1861.

Fort Macon, NC - 10 In Siege Mortar Model 1861
10-inch Model 1861 Siege Mortar

Published by Craig Swain

"Historical marker hunter" and Civil War enthusiast.

6 thoughts on “Iron Frogs: 8-inch Model 1861 Siege Mortars

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