Saphroneth
Banned
http://www.tank-net.com/forums/index.php?showtopic=17231&page=6#entry354576
A look at Fort Munroe and how the RN could reduce it. The answer is - "very easily". Ft. Munroe is rather inferior to Kinburn, since it's right by a deep water channel and as such liners and armoured frigates can get very close.
There's also this source:
https://books.google.co.uk/books?id...#v=onepage&q=hms edgar armstrong guns&f=false
Showing the Armstrong guns and their current positions as of August 1863 - later than I'd like, but it shows that by that point the RN had >600 of the RBL 110-lber Armstrongs alone. Either most of these had been manufactured by Mar 1862, or the British can produce two hundred RBL heavy guns a year of this type alone...
Now, as to attacking the Narrows forts.
Firstly, I think we can agree that a battery of field guns (12 lbers) is unlikely to do significant damage to a liner - they can endure and even win battles with forts which are dropping 8" shells on them every so often (as per Crimea). So the fort guns are mostly it.
The Terror or other British ironclads are essentially invulnerable to the Narrows forts. They can go where they please and shoot what they want - if the British felt it militarily necessary to destroy the New York dockyards, they could just have their ironclads run the forts and destroy everything in sight. Since their presence makes the answer really easy ("The ironclads destroy the forts"), then we should look at liners... and even there the answer is not good.
Depth wise, it's easy to get a good arc. There's areas with adequate low tide depth for a liner south of the forts and within (in some cases) 1/3 of a mile - ~500 yards, closest ideal RN bombardment range for a liner. (The Crimea ironclads can anchor about a hundred yards away, though they'd probably be more like 200-300, and the gunboats would try to find a position where the guns can't bear and then just blast away.)
8" shell hits from 500 yards are a possible risk to the ships, though several RN liners survived that kind of punishment in the Crimea. They're also able to fling back a lot more than is pointed at them.
The 32-lber guns are marginal to penetrate the wooden sidewalls of the RN ships (three feet of white oak, Dahlgren's tables show 38.5" theoretical penetration at 500 yards) and the 24-lbers are no-hopers.
So looking again at that table for reducing the forts from the south - let's say the liners anchor 800 yards away (half Kinburn, twice what they'd consider - they're being cautious). At this range a 32-lber penetrates about 28"-30", so the liners are not vulnerable to single penetration by 32-lbers.
The total south facing firepower of the forts is
63 32 lber
9 24 lber
Up to 20 8" guns
So there's 20 8" guns which can hurt the liners. In reply, picking seven of the liners on station:
Nile
Donegal
St George
Aboukir
Edgar
Hero
Sans Pareil
32 lber = 45 + 32 + 57 + 39 + 27 + 27 + 32 = 259
68 lber = 1 + 1 + 1 + 2 + 1 + 1 = 7
8" = 18 + 4 + 18 + 18 + 3 = 61
Even just looking at the 8" guns and dismissing everything else, there's three times as many guns afloat per broadside as on the forts. This is sufficient to reduce a fort in the age of sail (3 afloat = 1 ashore) let alone in the age of steam (1 afloat = 1 ashore) - and this is just the heavy ships, not the gunboat cloud the RN normally deployed.
But the gunboats raise a further point. The RN doesn't actually need to enter the firing arc of the forts at all.
RN gunboats served all over the world OTL, and they had a lot of them. The typical RN gunboat mounted either a 68-lber or a 110-lber RBL, both of which outrange the forts... and both of which are good bombardment pieces, either due to sheer muzzle velocity for punching or because they fire large shells (9") a long way with rifle-type accuracy. These are augmented by the (see source on Armstrong locations) guns mounted on several of the liners. In 1863 Edgar mounted
1x 6 pdr 1x 12 pdr, 2 x 20 pdr, 16x 40 pdr and 2x 110 pdr Armstrongs
all of which can outrange the forts, and the 40 lber and 110 lber are somewhat or considerably more powerful than the 32 lbers making up most of the fort armament.
And on top of all that the RN has mortar floats it can deploy, which will also be quite competent to destroy forts as per Bomarsund.
So...
...the RN has not one but at least four distinct ways to neutralize the Narrows forts for comparatively low risk, even if large numbers of US soldiers are moved in to prevent a simple landing:
1) Liner bombardment at 500-600 yards
2) Ironclad bombardment from very close range
3) Rifled heavy guns engaging from outside the range of the US forts
4) Mortar floats barraging the fort at long range
All of these except (3) can be accompanied by the opportunistic gunboat swarms the RN used against pretty much the entire Sea of Azov coastline, and the likely initial plan once reinforcements and gunboats show up is to plan for a week and then do a combined assault (liners at ~800 yards, frigates at ~700, gunboats everywhere, mortars at ~1000 yards and the ironclad/s anchoring inside 200 yards. The forts are taken under an even heavier bombardment than the one which neutralized Kinburn in the space of three hours, and even in the most pro-US calculation are likely to fall in a day or two.
Then the RN can destroy or capture basically whatever they want to in New York.
n.b. post Gettysburg BG Barnard:
https://markerhunter.wordpress.com/category/battlefields/fort-washington/
Concluded nothing on the Potomac inland of Fort Monroe could hurt an ironclad.
A look at Fort Munroe and how the RN could reduce it. The answer is - "very easily". Ft. Munroe is rather inferior to Kinburn, since it's right by a deep water channel and as such liners and armoured frigates can get very close.
There's also this source:
https://books.google.co.uk/books?id...#v=onepage&q=hms edgar armstrong guns&f=false
Showing the Armstrong guns and their current positions as of August 1863 - later than I'd like, but it shows that by that point the RN had >600 of the RBL 110-lber Armstrongs alone. Either most of these had been manufactured by Mar 1862, or the British can produce two hundred RBL heavy guns a year of this type alone...
Now, as to attacking the Narrows forts.
Firstly, I think we can agree that a battery of field guns (12 lbers) is unlikely to do significant damage to a liner - they can endure and even win battles with forts which are dropping 8" shells on them every so often (as per Crimea). So the fort guns are mostly it.
The Terror or other British ironclads are essentially invulnerable to the Narrows forts. They can go where they please and shoot what they want - if the British felt it militarily necessary to destroy the New York dockyards, they could just have their ironclads run the forts and destroy everything in sight. Since their presence makes the answer really easy ("The ironclads destroy the forts"), then we should look at liners... and even there the answer is not good.
Depth wise, it's easy to get a good arc. There's areas with adequate low tide depth for a liner south of the forts and within (in some cases) 1/3 of a mile - ~500 yards, closest ideal RN bombardment range for a liner. (The Crimea ironclads can anchor about a hundred yards away, though they'd probably be more like 200-300, and the gunboats would try to find a position where the guns can't bear and then just blast away.)
8" shell hits from 500 yards are a possible risk to the ships, though several RN liners survived that kind of punishment in the Crimea. They're also able to fling back a lot more than is pointed at them.
The 32-lber guns are marginal to penetrate the wooden sidewalls of the RN ships (three feet of white oak, Dahlgren's tables show 38.5" theoretical penetration at 500 yards) and the 24-lbers are no-hopers.
So looking again at that table for reducing the forts from the south - let's say the liners anchor 800 yards away (half Kinburn, twice what they'd consider - they're being cautious). At this range a 32-lber penetrates about 28"-30", so the liners are not vulnerable to single penetration by 32-lbers.
The total south facing firepower of the forts is
63 32 lber
9 24 lber
Up to 20 8" guns
So there's 20 8" guns which can hurt the liners. In reply, picking seven of the liners on station:
Nile
Donegal
St George
Aboukir
Edgar
Hero
Sans Pareil
32 lber = 45 + 32 + 57 + 39 + 27 + 27 + 32 = 259
68 lber = 1 + 1 + 1 + 2 + 1 + 1 = 7
8" = 18 + 4 + 18 + 18 + 3 = 61
Even just looking at the 8" guns and dismissing everything else, there's three times as many guns afloat per broadside as on the forts. This is sufficient to reduce a fort in the age of sail (3 afloat = 1 ashore) let alone in the age of steam (1 afloat = 1 ashore) - and this is just the heavy ships, not the gunboat cloud the RN normally deployed.
But the gunboats raise a further point. The RN doesn't actually need to enter the firing arc of the forts at all.
RN gunboats served all over the world OTL, and they had a lot of them. The typical RN gunboat mounted either a 68-lber or a 110-lber RBL, both of which outrange the forts... and both of which are good bombardment pieces, either due to sheer muzzle velocity for punching or because they fire large shells (9") a long way with rifle-type accuracy. These are augmented by the (see source on Armstrong locations) guns mounted on several of the liners. In 1863 Edgar mounted
1x 6 pdr 1x 12 pdr, 2 x 20 pdr, 16x 40 pdr and 2x 110 pdr Armstrongs
all of which can outrange the forts, and the 40 lber and 110 lber are somewhat or considerably more powerful than the 32 lbers making up most of the fort armament.
And on top of all that the RN has mortar floats it can deploy, which will also be quite competent to destroy forts as per Bomarsund.
So...
...the RN has not one but at least four distinct ways to neutralize the Narrows forts for comparatively low risk, even if large numbers of US soldiers are moved in to prevent a simple landing:
1) Liner bombardment at 500-600 yards
2) Ironclad bombardment from very close range
3) Rifled heavy guns engaging from outside the range of the US forts
4) Mortar floats barraging the fort at long range
All of these except (3) can be accompanied by the opportunistic gunboat swarms the RN used against pretty much the entire Sea of Azov coastline, and the likely initial plan once reinforcements and gunboats show up is to plan for a week and then do a combined assault (liners at ~800 yards, frigates at ~700, gunboats everywhere, mortars at ~1000 yards and the ironclad/s anchoring inside 200 yards. The forts are taken under an even heavier bombardment than the one which neutralized Kinburn in the space of three hours, and even in the most pro-US calculation are likely to fall in a day or two.
Then the RN can destroy or capture basically whatever they want to in New York.
n.b. post Gettysburg BG Barnard:
https://markerhunter.wordpress.com/category/battlefields/fort-washington/
Concluded nothing on the Potomac inland of Fort Monroe could hurt an ironclad.