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

Rhea Cole

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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.
 
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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.
IIRC, the Passaics were supposed to have two XV-inch Dahlgrens but there were production problems, so they substituted a mixed battery (as we know, the original Monitor had two XI-inch Dahlgrens). I think the Canonicus class finally went to two XV-inch.
 
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IIRC, the Passaics were supposed to have two XV-inch Dahlgrens but there were production problems, so they substituted a mixed battery (as we know, the original Monitor had two XI-inch Dahlgrens). I think the Canonicus class finally went to two XV-inch.
When they fitted 15” guns, they had to shave the muzzles so that they would fit through the gunports.
 
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If I recall correctly, Dahlgren championed the XIII-inch for these monitors and Ericsson designed the class with them in mind. The XV-inch was a decision made at the departmental level, possibly by Gustavus Fox, and neither Dahlgren nor Ericsson were entirely happy about it. As it was, production shortages of the XV-inchers meant that most of the Passaics were armed with one and one XI-inch; the XI-inch had to be fitted to a mounting meant for a larger gun, and the XV-inch was too big to fit through the port, so it was actually fired entirely inside the turret (with a "smoke box" built up around it to try to minimize the smoke within the turret).

One monitor (I think the Patapsco) had a 150-pounder Parrot rifle instead of the XI-inch; and the Camanche earmarked for the West Coast and delayed in construction, had two XV-inch, with gunports large enough to fit them.

passaic1q.jpg



(The slow rate of fire of the XV-inch also bogged down the otherwise-quicker XI-inch. I wonder how things would have gone had they been allowed to stick with the original twin XIII-inch plan.)
 
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If I recall correctly, Dahlgren championed the XIII-inch for these monitors and Ericsson designed the class with them in mind. The XV-inch was a decision made at the departmental level, possibly by Gustavus Fox, and neither Dahlgren nor Ericsson were entirely happy about it. As it was, production shortages of the XV-inchers meant that most of the Passaics were armed with one and one XI-inch; the XI-inch had to be fitted to a mounting meant for a larger gun, and the XV-inch was too big to fit through the port, so it was actually fired entirely inside the turret (with a "smoke box" built up around it to try to minimize the smoke within the turret).

One monitor (I think the Patapsco) had a 150-pounder Parrot rifle instead of the XI-inch; and the Camanche earmarked for the West Coast and delayed in construction, had two XV-inch, with gunports large enough to fit them.

View attachment 421455


(The slow rate of fire of the XV-inch also bogged down the otherwise-quicker XI-inch. I wonder how things would have gone had they been allowed to stick with the original twin XIII-inch plan.)
This does look a bit on the demented side. What I still don’t understand is why they didn’t put two 11” or 15” instead of doubling them up. Something’s are simply not meant to be understood.
 
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If I recall correctly, Dahlgren championed the XIII-inch for these monitors and Ericsson designed the class with them in mind. The XV-inch was a decision made at the departmental level, possibly by Gustavus Fox, and neither Dahlgren nor Ericsson were entirely happy about it. As it was, production shortages of the XV-inchers meant that most of the Passaics were armed with one and one XI-inch; the XI-inch had to be fitted to a mounting meant for a larger gun, and the XV-inch was too big to fit through the port, so it was actually fired entirely inside the turret (with a "smoke box" built up around it to try to minimize the smoke within the turret).

One monitor (I think the Patapsco) had a 150-pounder Parrot rifle instead of the XI-inch; and the Camanche earmarked for the West Coast and delayed in construction, had two XV-inch, with gunports large enough to fit them.

View attachment 421455


(The slow rate of fire of the XV-inch also bogged down the otherwise-quicker XI-inch. I wonder how things would have gone had they been allowed to stick with the original twin XIII-inch plan.)
A good question! We must keep in mind that the IX, XI and XV Dahlgren's were 'shell' guns, as were all the Parrott guns. These were intended to lob explosive shell using small to moderate charges. The XIII Dahlgren was proportionately longer, and was intended to be a 'shot' gun of moderate performance against armor. That later in the war the XV Dahlgren enjoyed some success against armor was due primarily to the change in production techniques, from solid cast to Rodman's hollow cast, which made for a gun strong enough to handle large charges without bursting.
 
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Consider, how do you aim?

If you had 2 15" guns, with their smokeboxes, there is no way to look out and at least shoot in roughly the right direction.

The slow rate of fire of the 15" was partially caused by the fact that no supply of ammunition could be kept in the turret. There was a rack for 11" balls, which could just about be hand loaded by several people, but there was no way of moving a 15" ball by hand. The balls were moved completely by winch, and stored below the turret. To load the 15", the turret has to locate to a position where the hatches are aligned, and then open the hatches, and winch down the loading device, winch it back up etc.
 
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If I recall correctly, Dahlgren championed the XIII-inch for these monitors and Ericsson designed the class with them in mind. The XV-inch was a decision made at the departmental level, possibly by Gustavus Fox, and neither Dahlgren nor Ericsson were entirely happy about it. As it was, production shortages of the XV-inchers meant that most of the Passaics were armed with one and one XI-inch; the XI-inch had to be fitted to a mounting meant for a larger gun, and the XV-inch was too big to fit through the port, so it was actually fired entirely inside the turret (with a "smoke box" built up around it to try to minimize the smoke within the turret).

One monitor (I think the Patapsco) had a 150-pounder Parrot rifle instead of the XI-inch; and the Camanche earmarked for the West Coast and delayed in construction, had two XV-inch, with gunports large enough to fit them.

View attachment 421455


(The slow rate of fire of the XV-inch also bogged down the otherwise-quicker XI-inch. I wonder how things would have gone had they been allowed to stick with the original twin XIII-inch plan.)
This photo really puts some perspective on the size of these monsters
 
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A good question! We must keep in mind that the IX, XI and XV Dahlgren's were 'shell' guns, as were all the Parrott guns. These were intended to lob explosive shell using small to moderate charges. The XIII Dahlgren was proportionately longer, and was intended to be a 'shot' gun of moderate performance against armor. That later in the war the XV Dahlgren enjoyed some success against armor was due primarily to the change in production techniques, from solid cast to Rodman's hollow cast, which made for a gun strong enough to handle large charges without bursting.
Interesting points. To follow up on the mixed XI-inch/XV-inch batteries, given the production issues Dahlgren actually favored using uniform XI-inch batteries on the Passaics but Ericsson was in love with the bigger gun - especially given the USN's tactical focus at the time on attacking Charleston - and so he won out on this. It's a good example of the "ship design" side (later BuShips) winning out over the ordnance side (BuOrd), pressed by strategic considerations. Dahlgren had proofing concerns about the XV-inch guns being turned out and also gave it a service life that was approximately one-third that of both the IX and XI-inch guns. He kept pushing smooth bores after the war but lost out based on the efficacy of big rifles developed by other navies.
 
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Interesting points. To follow up on the mixed XI-inch/XV-inch batteries, given the production issues Dahlgren actually favored using uniform XI-inch batteries on the Passaics but Ericsson was in love with the bigger gun - especially given the USN's tactical focus at the time on attacking Charleston - and so he won out on this. It's a good example of the "ship design" side (later BuShips) winning out over the ordnance side (BuOrd), pressed by strategic considerations. Dahlgren had proofing concerns about the XV-inch guns being turned out and also gave it a service life that was approximately one-third that of both the IX and XI-inch guns. He kept pushing smooth bores after the war but lost out based on the efficacy of big rifles developed by other navies.
I have never seen anything larger than 12 pounds live fired. There is something toe curling about being locked up in a turret with a XV” gun when it went off... yahoo! from a respectful distance any day.
 
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I have never seen anything larger than 12 pounds live fired. There is something toe curling about being locked up in a turret with a XV gun when it went off... yahoo! from a respectful distance any day.
Here's the bright side - you wouldn't be stepping around bags of cordite laying all over the place, unlike the poor wretches serving on HMS Indefatigable and Queen Mary when they blew up at Jutland. As Vice-Admiral Beatty allegedly observed, "There seems to be something wrong with our bloody ships today".
 
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Here's the bright side - you wouldn't be stepping around bags of cordite laying all over the place, unlike the poor wretches serving on HMS Indefatigable and Queen Mary when they blew up at Jutland. As Vice-Admiral Beatty allegedly observed, "There seems to be something wrong with our bloody ships today".
The turret casualty on the Iowa also comes to mind…
 
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The turret casualty on the Iowa also comes to mind…
Yep. If I recall correctly, there was never agreement on the final cause. I think some outside outfit ultimately decided it was an over-ramming issue, but the USN never came to a result after moving on from the early sabotage theory. (That's based on memory, so I might have the details wrong.)

The battlecruiser problem at Jutland was almost certainly the sloppy storage and handling of cordite, which was a result of the Royal Navy's obsession with rapid fire, made worse by the light turret armor in the BC design for speed rather than protection. One irony is that Beatty's own flagship HMS Lion nearly suffered the same fate as the other two when its Q turret was hit but some quick-thinking courageous crew kept all that loose ammo from going up. The Germans used a safer method of packing and storing which suited their more deliberate fire doctrine.
 
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Yep. If I recall correctly, there was never agreement on the final cause. I think some outside outfit ultimately decided it was an over-ramming issue, but the USN never came to a result after moving on from the early sabotage theory. (That's based on memory, so I might have the details wrong.)

The battlecruiser problem at Jutland was almost certainly the sloppy storage and handling of cordite, which was a result of the Royal Navy's obsession with rapid fire, made worse by the light turret armor in the BC design for speed rather than protection. One irony is that Beatty's own flagship HMS Lion nearly suffered the same fate as the other two when its Q turret was hit but some quick-thinking courageous crew kept all that loose ammo from going up. The Germans used a safer method of packing and storing which suited their more deliberate fire doctrine.
In Dreadnaught the garrison thinking that came from a century of peacetime bandbox pseudo drill had resulted the removal of the safety doors between the turret & magazine. Like re-enactments, the emphasis was on the speed of fire. Like re-enactments, ignoring the safety procedures, in order to quick fire in this case actually disabling them, led to disaster. In some cases, the over gunned battle cruisers suffered major structural damage from recoil of their own guns.

It was the dying action of the Marine officer in the magazine that saved Beatty’s ship. It was the remains of that turret that enabled the court of inquiry to discover the self inflicted failure that doomed the battle cruisers.
 
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In Dreadnaught the garrison thinking that came from a century of peacetime bandbox pseudo drill had resulted the removal of the safety doors between the turret & magazine. Like re-enactments, the emphasis was on the speed of fire. Like re-enactments, ignoring the safety procedures, in order to quick fire in this case actually disabling them, led to disaster. In some cases, the over gunned battle cruisers suffered major structural damage from recoil of their own guns.

It was the dying action of the Marine officer in the magazine that saved Beatty’s ship. It was the remains of that turret that enabled the court of inquiry to discover the self inflicted failure that doomed the battle cruisers.
Good points - removal of the safety doors was a problem, although the big issue was that they literally had cordite stashed everywhere. Some dives in the last 15 years or so - at least on QM - appear to have confirmed this and account for the likely site of her secondary explosion.
 
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Re the mixed battery monitors, was the firing rate difference between the 15in and 11in guns different enough to matter, operationally? Weren’t both, as a practical matter, quite slow firing? The need to retrain the turret to reload seems like a real pain, makes you wonder if a barrette or casemate might have been a better choice for a mounting.

It’s interesting to ponder the differences Armstrong type breachloaders might have made on performance… probably not much, given their general unreliability, but then I seem to recall some post-war modifications of Monitors getting breachloaders. I want to say it was the Onondaga that got 9 in breachloaders in French service?
 
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