Why Were Monitors' Turrets Armed With Both 11" & 15" Cannons?

Rhea Cole

Major
Joined
Nov 2, 2019
Location
Murfreesboro, Tennessee
Interior turret Passaic.jpeg

Interior of the turret of USS Passaic.

The difference in size between the 11" & 15" Dalghren smoothbores is obvious. not obvious is why one of each in the turret?​

Monitors were armed with one 11" & one 15" Dahlgren cannons. What was the point of that? Late in the war, the 11" was replaced with an 8" rifle, which makes some sense. Anyways, it seems illogical to complicate the magazine storage & logistic support with two caliber of smoothbore cannon. Both guns could only be elevated to 5 degrees. I know of no advantage of one gun over the other or what the point of the combination was.
 
Last edited:
As indicated, it was shot with a hollow core (during manufacture the core was sand, which was then removed). The theory was reduced weight resulting in reduced stress, while at the same time getting increased velocity. Also as indicated, in theory it was intended for use against masonry.
A friend of mine was involved in manufacturing depleted uranium fletchettes for tank rounds. They used the breech of a 16” naval cannon in the process. Interesting link to tradition, no?
 
Vote Here:
It is interesting to note that when they were launched in 1915 the ultra modern USS Texas & USS New York carried 14 “anti-destroyer guns” mounted in her hull. There was even one protruding from the narrow stern. They were removed during the battleships' first refit.
USS Texas was launched in 1912 and commissioned 1914. USS New York was also launched 1912 and commissioned 1914.
They also had at least one significant lack of modernity, which was that they had triple-expansion steam engines - some of the few Dreadnought Battleships to do so. (All British dreadnoughts had turbines, and so did German ones starting before the Texas and New York were built.)

The anti-destroyer armament was 21 guns as first built. They were reduced at the first refits, but not eliminated; it's not surprising they weren't eliminated because they served an important purpose.


The Onadonga was indeed rearmed with 9.4” rifles when she entered French service. The turret was tactically superior to the casement design. For 1/2 of the guns to bear a casement had to be maneuvered onto a parallel course. At an oblique angle of approach, none of the casement broadside batteries could be brought to bear on a target. For a casement to have 360 degree firepower, two guns would have to be mounted fore, aft & both sides which necessitated a large, heavy structure.

A turret ship like Onadonga could bring all four of her guns to bear on 360 degrees of approach or departure except for dead on fore or aft. That gave the double turreted Monitor a freedom of maneuver that was far superior to a barbette.
I think you mean superior to a casemate in that last sentence; a barbette in warship design is an "unarmoured turret" that can rotate.

Based on doing some modelling, it looks like the front arc where only one turret can fire is 25 degrees across, which is fair enough. Though the sense I get looking at period warship design (Warrior to Dreadnought) is that oblique fire from a casemate was a flexible thing - and of course one great advantage of a casemate is that it's much easier to have a masted casemate ship than a masted turret ship, giving easier worldwide mobility in the days before coaling stations and highly efficient steam engines.
 
Vote Here:
Cored shots were shots with a hollow cavity at the core, rather than being solid iron balls. They were heavier than a shell (because the cavity was smaller) but lighter than a solid ball.

A 400 pound cored shot with 50 lbs powder was propelled at an initial velocity of 1,200 feet per second, while a 440 pound solid shot with 60 lbs powder was propelled at 1,230 feet per second.

I do not know why they bothered with cored shot, as it reduces the penetrating power of the shot and has no countervailing advantages in combat. Possibly it was manufacturing problems with the solid shot.




That range isn't really meaningful though because there's no way to reliably hit at that range. What matters for period smoothbore is the ability to hit the target at that range, because that is the limiting factor.


Though that's a completely different nature of weapon to a Civil War era black powder cannon. In particular they fire fin-stabilized darts which (to my understanding) slide down the barrel, while a Civil War gun fires round balls which bounce down the barrel; the accuracy is quite different because the Civil War smoothbore fires a projectile with no inherent stabilization and the last bounce is random.
I am pretty sure Iron Clads had counter battery operations against forts and fortifications where they could fire and hit a stationary target at those ranges.
 
Vote Here:
Cored shots were shots with a hollow cavity at the core, rather than being solid iron balls. They were heavier than a shell (because the cavity was smaller) but lighter than a solid ball.

A 400 pound cored shot with 50 lbs powder was propelled at an initial velocity of 1,200 feet per second, while a 440 pound solid shot with 60 lbs powder was propelled at 1,230 feet per second.

I do not know why they bothered with cored shot, as it reduces the penetrating power of the shot and has no countervailing advantages in combat. Possibly it was manufacturing problems with the solid shot.




That range isn't really meaningful though because there's no way to reliably hit at that range. What matters for period smoothbore is the ability to hit the target at that range, because that is the limiting factor.


Though that's a completely different nature of weapon to a Civil War era black powder cannon. In particular they fire fin-stabilized darts which (to my understanding) slide down the barrel, while a Civil War gun fires round balls which bounce down the barrel; the accuracy is quite different because the Civil War smoothbore fires a projectile with no inherent stabilization and the last bounce is random.
All but one round used in the Abrams smooth bore have no stabilizing fins. I know its very different technology from the ACW
 
Vote Here:
I am pretty sure Iron Clads had counter battery operations against forts and fortifications where they could fire and hit a stationary target at those ranges.
Well, if bombarding a large stationary fort then obviously that changes - but what we'd actually expect for a ballistic arc for a 1200 fps projectile at 7 degrees elevation (cored shot for a 15" at 50 lbs for example) is a peak at about 2000 metres, at which point the projectile is 120 metres above the firing point. This isn't really any kind of expression of maximum range, of course.

I wonder if there were actual range tests done? You'd sort of expect it to happen during acceptance, but I believe that wasn't US(N and A) practice.

In the actual bombardments of Fort Sumter etc, the hit rates aren't very good to my understanding and that's at 600-1000 yards. Though this may be partly because the 15" can't be aimed on a Passaic except by sighting down the 11" next to it and hoping they're pointing parallel!
 
Vote Here:
Back
Top