Yeah, but if we could have lured them onto the Mississippi or Charleston Harbor they’d’ve been in BIG trouble. Monitors may not be seaworthy but they’re wicked hard to hit! 
/Hijack: one of my proudest moments was finding a very tacky circa 1950s pressed glass ashtray, with a photo of the U.S.S. Cairo, the whole thing then being countersunk into a largish 6" by 6" worm-eaten chunk of that ill-fated monitor’s framework. It cost me a whopping $25 at a local junk emporium, and I found it just days before the 30th anniversary of the guy I work with starting here at the Fort–he’s the orginal Civil War buff nonpareil. Our search for an appropriate gift was at an end.
Trouble is, he’s still working here–and September will mark his 40th year. Where the hell I am going to find something to top that?
(And how did a piece of the “Kay-row” find its way up here?)
//Hijack ends
The first Ironclad had been build a dozen years ago by the french navy, and used during the Crimea war. By the time of the american civil war, both France and the UK had seaworthy ironclads.
Regarding the OP, the first question to ask would be : Mexico excepted, what reasons could have other countries to attak the USA, exactly? What would have been the point?
What was the thickness of the armor on the French and British ironclads? Both North and South had projectiles (some were of british design) that could penetrate four inches of wrought iron.
This article, in the Journal for Maritime Research gives her iron armour as four and a half inch, back by two layers of teak:
http://www.jmr.nmm.ac.uk/server/show/conJmrArticle.14/setPaginate/No
I should add that my link refers to HMS Warrior. Of course, she was armed with 10 of the the rather less-than reliable Armstrong 110 pr rifled breech-loaders, which had the alarming propensity to blow up in the crew’s faces at times.
Two years after she was first commissioned, the 10 Armstrong RBLs were sold off…to the Confederate States of America.
The Monitor had double that- and later monitors had triple that- with much larger guns, placed in two turrents. And, they were very difficult targets to hit, too. If the Warrior was in close to the shore, one of our double-turrented monitors could sink it with impunity- and outmanuever it, also. And we had squadrons of monitors. Their guns would go right through 4" armour, and explod on the inside, causing immense destruction due to the splinters.
Sure, like I said- they couldn’t make it overseas unless they were lucky, but a squadron of “modern” Union Monitors could have sank the entire British armada easily, if the Brit’s tried to come over here.
Perhaps, perhaps not. But even that scenario is assuming stasis. Personally I have no doubt that given her vast resources and expertise at the time Britain would have been more than capable of handling a naval arms race with the Union, especially a Union still locked in combat with the Confederacy.
A moot point of course. As other posters have noted it would have taken an extremely unlikely course of events for such a conflict to develop.
- Tamerlane
Correct. The Union likely only had World naval superiourity for less than a decade, and GB could likely have cut that in half with a serious naval programme. Having the USA and GB in a naval building race would be a doubtful “alternate universe” , but interesting.
There are ways it could have- IF Lincoln hadn’t issued the Emancipation Proclamation, AND the Confederates promised to end slavery. The second is extremely doubtful. One of Harry Turtletaubs “Alternate history” books ends like this which places it firmly into fantasy. :dubious: If the President of the CSA had tried to do so, most of the Confederacy would have seceded again- from the CSA. IMHO. of course.
Confederates operating out of Canada raided the Union in Vermont and on the not so high seas of Lake Erie. Immediately after the war, Fenians (many of whom were Union vets), made several raids into Canada.
http://www.onwar.com/aced/data/charlie/canada1864.htm
http://www.history.navy.mil/danfs/cfa7/philo_parsons.htm
http://www.acsu.buffalo.edu/~dbertuca/g/FenianRaid.html
Read “Stars and Stripes Together” it explains this very well
12-7 X10,
that’s… 1270.
My God!
Is that a sequel or do you mean “Stars and Stripes Forever” a good book but as the review says perhaps a little Anglophobic 
All that and a bag of chips, these days. But in the 1860s we were the industrial colossus of the world, though not for very much longer. Like I say, why change a winning strategy?
This goes a long way towards explaining why, in History of the World, the United States is unable to cross the Atlantic. 