Explain forts and castles to me

Exactly. A castle or fortification exists just to keep the people inside safe. It’s the garrison inside that defends an area and maintains a presence. The castle is a tactical measure. The garrison provides the strategic means.

And the usual high towers are long range detection & signaling facilities.

Any gun you can place on a ship, you can place a bigger one in a land based fort-and a fort can’t sink.

Warfare is not simply a matter of two big armies lining up and going at it, the winner being declared the victor. There’s a lot of strategy involved. A massed army is very powerful, but it can only control the relatively small region it currently occupies. A dispursed army of small units can control a large region, but only if there is no major opposition force. Therein lies the power of the citadel or fortress. It creates a threat where if an army dispurses into smaller units to control a region, forces can attack those small units from the fortress and then retreat to the safety of their walls while the enemy is in makeshift camps. The fortress can send out troops to attack supply lines and rear areas and otherwise disrupt the plans of the invaders.
For the most part though, a castle was simply a fortified residence of the local fuedel lord. He could send his troops out to collect taxes from the peasents and they in return could do jack shit.

At long as you didn’t build your castle in a swamp.

One thing to recall about Fort Jefferson is that it was not intended as a solitary point. It was part of a ring that extended from Maine to Texas. While the “attack the rear” function would have been minimal for Fort Jefferson, (being an Army installation with no serious port from which to launch attacks), its presence would have denied the use of the Tortugas to any force which intended to use the islands as a point of rendezvous or for staging an attack against the mainland coast on the Caribbean.

When completed, the ring of forts was intended to deprive any opponent from getting a toehold on the U.S. coast. Fort Jefferson was probably designed to be the largest simply because it would have needed to be able to sustain itself for a longer siege than any of the forts built along the coast that could have been resupplied from the local towns

Actually, by the time of the Civil War, land-based defenses were not terribly effective, unless they had ample natural backing. Ships were exceptionaly tough and often capable of taking enough punishment that land-based guns were effectively no stronger: both sides’ gun crews would be killed before the structures broke. Obviously, there were differences depending on the specific equipment of both sides, but all in all manuverability was more important than armor until the invention of the ironclads. And the ironclads rapidly grew into fully mobile vessels.

Soon after, ship guns grew so powerful that land-based defenses couldn’t hope to hit them at the ranges they fired at.

In previous eras, land-based guns had not been enough to stop serious attacks.

Fort Nelson, [England] http://www.fareham.gov.uk/town/activities/places/fortnelson.asp is one of a chain of forts built in the 1860s on Portsdown Hill (actually a ridgeline) behind the City of Portsmouth. In this case their purpose was not to defend the harbour against hostile ships, in the era before air power this was best done with another ship, but to deny the ridge to an enemy landing on a flank, marching around the back of the town and establishing batteries on the ridge to bombard the town and the navy yard. Enemy will have to subdue the forts before he can make use of the ridge, which buys time for reinforcements to arrive.

Thanks for posting that link! I’m going there on Trafalgar day and needed that info.

As has been said before, a Fort is a handy place to keep supplies and a relatively safe place for friendly troops to camp out for the night. You can just stack supplies up over an extended period of time in a place where it’s difficult for a fast-moving enemy raiding party to steal or destroy them. A moving enemy force can’t do any of this until it secures it’s own strongpoint. (If they’re near the water, a squadron of ships can serve this purpose, but only until another force of ships (or in later years, aircraft) is able to chase them off.

Also, in the case of coastal forts, defenseless merchant or transport ships will often run along the coast from fort to fort, sailing by night and hiding in the shade of friendly cannon by day (this practice continued as late as World War II in the Gulf of Mexico, with oil tankers from Texas coasting their way along the Gulf coast and up the East coast trying to avoid German U-Boats.)

And also for coastal forts, even if larger warships can’t dock at or near the forts, they can coordinate their efforts with the fort, maneuvering to force an enemy force in close to the fort where they would be harried both by coastal fire and by gunboats launched from shore (imagine a really big rowboat, with a really big cannon or two in the bow and some lighter guns along the sides) all while trying to avoid being run aground by the seaward force.

Forts have their limitations though. Oftentimes it’s due to advanced in technology or unforseen circumstances at the time of their construction. For example, Fort Sumtner was designed to resist a force attacking from sea, as it was assumed the other forts in the harbor would be supporting it, rather than attacking it. This wasn’t the case when the Civil War started though. During the same war, Union steamships using new rifled cannon were able to shell Confederate forts while they themselves were able to stay safely out of range of the defenders’ weapons.

Thsi was in fact a favoured strategy by French forces in their fight against English armies during the Hundred Years’ War.

I’d like to point out that there’s a difference between a fort and a fortress.

Wait for it…

A fortress has breastworks.

I guess someone never watched The Guns of Navarone?

FYI – a set of very useful forts defend the only entrance to the bay at Cartagena, Colombia. Ships have to pass through a fairly narrow channel, with a fort on top of a hill on either side. Basically, canons to the left and right, shooting down on any unwanted boat trying to get in.

So sometimes they really can defend a specific area.

Oh, they weren’t entirely useless. But the nature and scale of war keeps increased throughout history until WW2, after which is shrank. Small-scale fortresses simply couldn’t expand as much as an enemy flotilla or army could. A fleet or corp can always call up another hundred guns or so. A fortress probably can’t.

Think about the naval attempt to force the Narrows at the Dardanelles in WWI. Initially, the British and French fleet seemed to be very effective against the fortresses defending the entrance. Eventually, in particular due to the reinforcement of mobile howitzer batteries, the defenses proved to be too much for the fleet (minefields also played a serious role, but the batteries, both fixed and mobile, prevented any mineclearing attempt from getting very far).

The fortesses didn’t match the size of the guns of the fleet, but they proved far more difficult to sink and damage than the ships.

In WWI and later into WWII, the mobility of defensive forces became a more powerful advantage than the survivability of fixed defenses (this wasn’t always appreciated, the Maginot Line is a good example, and the US continued to work on fixed coastal defenses until 1943). No matter how much concrete you place into your fortess, by WWII artillery and air power was enough to make you regret continuing to sit there.

After WWII, nuclear weapons also contribute to the mix, making even incredibly hardened fortresses like NORAD’s Cheyenne Mountain expect to be destroyed in a nuclear exchange.