Third System Fortress Engineering



 

 

 

 



On this page, you'll find some features common to almost all forts of the Second and Third Systems. The best way to find out about this stuff is to take Ranger or docent guided tours of them. They really know their forts and will bring out details you'll never see on a self-guided tour.

Basic Construction

 

These plain looking pictures show one of the more interesting and least known features of fort building - brick patterns. Specifically, look at the rows of long and short bricks.

The photo on the left is a Queen pattern.  The rows alternate short-long.  The short bricks are whole bricks placed in lengthwise.  This is the strongest pattern in building and was used for weight bearing walls and arches. It takes a lot of bricks, though.

On the right is the King pattern - long, long, long, short. It's not as strong but uses much fewer bricks. It was used for standard construction and floors. You'll see both of these basic patterns throughout all brick forts, including several variations of the King pattern.

 

 

These two photos are examples of casemates. Casemates are covered areas protected by heavy brick or stone construction from both direct and indirect fire. "Casemated construction" , with its many angles and arches, was the cornerstone of all forts of the era. The arch is the most basic part of casemate design. Arches can support much more weight than a flat overhead because they distribute weight across the whole arch and down the sides. Flat overheads bears all the weight within their own area.  Arches can also absorb more damage and still maintain structural integrity.

The casemate on the left is a passageway to allow soldiers to move about the fort during an attack.

The casemate on the right is a firing casemate. Both cannon and rifles could be fired through firing apertures around the left of the arch. (An example is shown below in the Guns section.) Large heavy wooden doors with rifle slots could close off these casemates into independent fighting positions if the enemy broke through. The large casemates on the right were also used as storage, guardhouses, sleeping areas, kitchens and prison cells.

 

 

Here are two more examples of casemates.  These are both from Fort Pickens but will be seen at all system forts. 

On the left are the large firing casemates seen from the inside of the fort looking outward.  You can clearly see the firing apertures and the arches.  The doors are long gone, removed for safety reasons. Above the casemates is the parapet with a cannon mounted on it.  This particular cannon is a 10 inch Rodman smooth bore weighing almost eight tons.  There were a dozen of them lined up on this parapet, giving you an idea of the strength of the construction.  They were fixed in position, held in place by steel pins. They could traverse left and right with steel wheels on rails, giving them a field of fire of almost 180 degrees. 

On the right is a cross section of a casemate, courtesy of an exploding powder magazine in 1899.  This is the same casemate as the photo on the left and is just off the right hand side of that photo.  Note the thickness of the walls and the layer upon layer of bricks. Fort Pickens consumed over 21 million of them. You can also see the parapet.  The 10 inch Rodman is further down the line.

Details and Craftsmanship

 

 

This photo contains a feature that blew me away and would be totally missed unless it was pointed out to you. Brick forts look very solid and connected - right? Wrong!  In this arched passageway, you can see a thin black line going down the center of the picture. That is a space between the interior of the fort and the outer wall. Turns out, they aren't connected at all. The wall is built first, then the interior is constructed inside of it. There are two reasons for this. It allows the masonry to flex in response to heat, cold and humidity. Without that flexing, a rigid, solid brick fort would tear itself apart. It also helps limit battle damage. If a wall or an arch collapses, it won't cause everything else attached to it to cave in.  Look for these spacers in all forts. They aren't cracks caused by age or shifting. They are built in by design.

 

This photo shows the entrance to a powder magazine, the most vulnerable area of the fort. Most forts cannot survive the explosion of a powder magazine, so builders went to great lengths to eliminate in house hazards like sparking and sabotage. The floors, walls and ceilings are made of wood, fastened with wooden pegs instead of nails. The door is wood also. All bars, hinges and locks are made of brass, which doesn't spark. Inside, everything is wood. Men working inside didn't wear boots.  The door was kept locked and stores handed out through the opening on top of the door. Since they were deep inside the fort, lighting was a challenge. The solution? Candle lanterns.  Made of brass. Lit outside the room and very carefully placed.

 

 

The craftsmanship in these forts is unbelievable. You see it everywhere but here are a couple of examples.  All of these edge bricks forming the archways had to be hand cut and fitted. Even the smaller forts like Gaines and Barrancas required millions of bricks. Large ones like Pickens and Morgan used tens of millions. Arches, doorways, turns, stairwells, firing apertures, vents and other components required special attention like that seen here. The number of custom bricks had to be in the tens of thousands. Many of these forts have survived storms, floods, erosion, climate extremes and other hazards for well over a century.  In some cases, the original cement has fallen away.  Yet the forts stand solidly because of the quality of masonry that went into them.

Defenses

 

 

It may not look like it but you are approaching a brick fort,  bristling with guns and men, from the land side. This is called the "glacis." It is a dirt slope built up against the outermost wall to shield it from direct fire and observation. You can also get the same effect by digging the fort into the ground, instead of on top of it. The disadvantage of a glacis is that it prevents the use of layered cannon to defend from land attack. Some of the glacis of these forts is so good you can't even tell you're walking up on something until you're right on top of it. This one, at Fort Barrancas, is pretty good at that. You won't see any glacis on the seaward side of a fort.  The multiple layers of cannon are necessary to engage their main target - enemy ships. Attacking ships will have a clear view of the seaward side of the fort.

 

Coming over the top of the glacis, this is what you would be confronted with. Awaiting you is a long steep drop into a dry moat taking rifle and cannon fire from three sides.  The steep drop down into the moat is called the "counterscarp." The wall of the fort is called the "scarp."  On top of that is the "parapet."  Note the firing apertures along the scarp. These would have shielded smaller, faster firing cannon, probably 12 pounders, spitting out canister and grapeshot as fast as they could.  There are also many rifle slots and there would have been guns and men on the parapet too. Obviously, this is not a good place to be attacking, which is one of the reasons it never happened. There would have been no escape. This dry moat is at Fort Pickens and was six to eight feet deeper than it is now.  This enabled the cannon and rifles to fire down into the moat instead of across at each other.

 

 

One of the weaknesses of single wall linear forts is that the closer you get, the less dangerous they become. As attackers rush the walls, it becomes harder and harder for the defenders to fire upon them. One of the ways Second and Third System forts addressed that weakness was through the use of bastions. These are reinforced blockhouses that project out beyond the perimeter wall but are still connected to the fort.  (A similar defensive structure not connected to the fort is called a redoubt.) This allowed them to bring fire to bear right along their own walls with cannon and rifle. The cannon would have been smaller caliber firing canister or grapeshot, turning them into giant shotguns. 

The photo on the left is a bastion at Fort Gaines, AL.  It had five of them - one on each corner of the pentagon-shaped fort. The main batteries were mounted en barbette on top of the bastions.  It guarded the western side of the entrance to Mobile Bay. Fort Gaines was a fairly small fort, built with six million bricks.  Its big brother, Fort Morgan, can be seen through the lamp posts.  It's about three miles away and was built with 20 million bricks.  Mobile is about 20 miles to the left of the picture. Off the right side of the picture is the Gulf of Mexico. The area between the two forts was the main battle area of the Battle of Mobile Bay on August 9, 1864. 

The photo on the right is the inside of this same bastion. The arch construction here is very complex and extremely well preserved. You can see firing apertures all around as well as a ventilation opening.  The circular insert in the middle is access to a cistern that gathered rain water.  Each bastion had one. A spiral staircase goes up to the eight ton 10 inch Rodman gun on top. Much of Fort Gaines was destroyed by a two day bombardment from both land and ships after the sea battle on August 9. With the walls breached and the ammunition storage exposed, the fort surrendered on August 8.  When they did, the Union called off its full blown ground attack scheduled for the next day. Then it was on to Fort Morgan, which held on for two more weeks.

Guns

 

 

This is parapet mounting of heavy cannon. In the language of fort building, firing over a parapet is called "en barbette." There are a couple of features common to forts of the era. The gun is mounted on granite, which won't crack or get grooves in it like brick. It has steel wheels on steel rails for movement.  Men using jacking bars can lever the gun around pretty quickly, even though this particular gun - a 15 inch Rodman - weighs 40,000 pounds. The carriage stays in place and the gun recoils to the back of it. This type of mounting gives the gun a 360 degree firing fan but offers scant protection for the crew. Also, it is a muzzle loader and the muzzle is higher than a man. This presents obvious difficulties, especially when trying to reload under fire.

 

This is a casemate mounted muzzle loading cannon.  It is also on a fixed carriage with steel wheels. The wheels run along a semi-circular track made of granite.  Some mounts like this will have rails on the granite. The gun recoiled along its own carriage which put it into position to be reloaded. Then it was cranked back into position for firing.  Even though it provides crew protection from enemy fire, it has hazards of its own.  One can only imagine the concussion and backblast produced in this confined space when the gun fired.  If the blast doors were closed and the casemate sealed up, it would be unbearable.

     
 

Here is another little feature built into the casemates. The photo is actually looking up at the ceiling over a casemated gun. That is a ventilation shaft.  In theory, smoke would go out and fresh air would come in.  No word on how those worked out.

 

The business end of a casemate mounted cannon.  This level is about head height on a man.  A gun here would have been used for close in defense and/or to fire at ships within range. The angled aperture gives the gun a bit of a range fan but not much. The muzzle would need to be extended more through the aperture so the blast would be directed outward. If the gun wasn't completely clear and/or nicked the brickwork when fired, it would be bad news for the crew.

I hope you've enjoyed this little pic-tour-ial and will get out and do some exploring.

Semper Fi...Out here...Alpha6