Attacking and Defending Forts



Inside a casemate at Fort Gaines. Note the firing embrasures for cannons and rifles.  The arch construction is much stronger than flat overheads and was used extensively in all forts of this type.  Each brick in the round part of the arch had to be cut and shaped to fit its spot. The spiral staircase in the far center leads up to one of the fort's main batteries, a ten ton cannon directly on top of this room. One can only imagine the heat, noise, flame, smoke and concussion that must have filled this bastion during battle.

People have built forts for both defense and power projection for thousands of years.  The most vital part of a fort is its walls. To keep attackers out and protect the people inside, walls were designed to counter the weapons they were most likely to face.  In the early days, that would have been arrows, spears and people - lots and lots of people.  To counter that, walls were quite high and the defense was close in.  As siege technology advanced, so did forts.  When battering rams and siege towers came along, so did moats. Forts were built on islands or on sheer rock faces.  Laying siege to a fortress was a lengthy process that might take months or even years.  Disease, hunger, thirst, morale and treachery became the main weapons.  Victory went to the side that held out the longest. The quickest way to overwhelm a fort is to get inside by breaching its walls,  but that capability was centuries in the making. Penetrating the walls required banging on the same place with something very heavy over and over and over again, which simply wasn't possible with the weapons of the day. This strategic stalemate continued for many centuries.

Then along came gunpowder.

Discovered accidentally late in the first century A.D. by Chinese alchemists looking for an "elixir of youth", the explosive propellant was quickly adapted for military use.  Weapons evolved quickly and simultaneously in many different cultures including the Chinese, the Japanese, the Muslims and the Europeans.  By the start of the 14th century, cannons, rockets and flame weapons firing projectiles were being used in both the attack and defense of forts.  Range, accuracy, power, types of shells and portability were still lacking, but the die was cast. The technology now existed to bang walls with something very heavy over and over and over again from long range. Forts and their tactics had to change to survive.

So walls became thicker and built out of harder material.  They also had to become lower and wider to support the new architecture.  This made forts more vulnerable to direct assault, so multiple walls were built inside one another.  In between walls were wet or dry moats. Bastions were created at corners and blind spots to allow flanking fire by both rifles and artillery against an enemy assault at the wall. 

Obstacles were placed on approach routes and covered by fire. Covered areas, called casemates, were built inside the fort to give the defenders overhead protection and the ability to move around while under fire.  Guns of various calibers were mounted in layers, with the casemate guns firing through embrasures and the top guns mounted "en barbette", meaning they were fired over a parapet.

Defenders started fighting outside the fort, deploying delay forces and extending the defensive perimeter. Multiple forts with overlapping fields of fire were used to protect key areas and each other.  Some forts were dug into the ground or covered with dirt and vegetation to mask themselves from enemy gunners.

 The dry moat at Fort Pickens, where attackers would be trapped on all sides by brick walls and gunfire.

The dry moat on the landward side of Fort Pickens on the east side of the entrance to Pensacola Bay. This kind of defensive barrier was found in all forts of this design and time frame. The original moat was eight to ten feet deeper than it is now.  This allowed the cannon to shoot down into the kill zone and not across at each other. A land assault would come over the wall on the right and down into a fire sack with canister rounds on three sides.   There would have been no escape.  A more likely tactic for the attackers would have been to bring up their own cannon on top of the outer wall and start blasting.  Anticipating that, some of the forts, including Pickens, built chambers underneath the outer wall to fill with explosives.  If an enemy ground assault started gaining traction, the wall they were firing from could be blown sky high. At least, that was the theory. However the laws of physics had other ideas.  The access to the explosives chamber would have been the weakest point of the design. Energy being expended always seeks the path of least resistance.  It's quite likely that a chamber full of explosives detonated under the wall would have blown back through the access hallway like a shaped charge, devastating the inside of the fort.  Since it was never done, we'll never know.

The attackers had two primary tactics - blast the walls into rubble and storm it and/or hammer the inside to the point where the fort surrendered.  To counter fort defenses against direct assault, the enemy would dig siege trenches which zigzagged towards the fort.  They would bring up their cannons and mortar when they were within range and start blasting.  They could continue to dig right up to the fort or even under it to set explosives.

American forts went through all these evolutions over the 150 years (1800-1950) they were in operation.  For the first 50-60 years,  the forts had the advantage.  A sailing ship bouncing around the water trying to catch the wind simply couldn't hope to outgun  or outrun the firing batteries of a strong coastal fortification. During the War of 1812, Baltimore's Fort McHenry fought it out with British forces that had just burned Washington D.C. The fort successfully turned back the British invasion and became the inspiration for "The Star Spangled Banner".

Then along came the American Civil War.

Friend and foe alike watched as the combatants on both sides advanced tactics and weapons more in four years than the rest of the world had done in the previous 100.  Larger caliber rounds, new fuses and increased accuracy of weapons doomed the forts.  Rifled projectiles, unlike the cannonballs of old, had enough penetration, kinetic energy and explosive power to blow apart masonry walls with one or two shots.


Damage from rifled cannon fire at Fort Pulaski in Savannah, Georgia.  Other parts of the wall were completely flattened.  Fort Pulaski was the last brick fort built by the U.S., much of it under the direction of 2nd Lt. Robert E. Lee, West Point Class of 1829.  In April 1862, it was the first fort to be attacked with new rifled cannon, which the Union  dragged through the surrounding swamps to get within range.  The results were devastating and rendered 1,000 years of military fortress engineering obsolete.  The defenders had laid in provisions for a six month siege.  They lasted two days, surrendering when Federal artillery breached the walls and started ranging in on the storage magazines where 20 tons of ammunition were kept. Some of the shells are still embedded in the walls. 





Ships were now steam powered, giving them the speed and maneuverability to minimize effective hits from shore batteries.  There were also ironclads.  Everyone has heard of the Monitor and the Merrimac.  They were 1862 prototypes that found themselves engaged almost by accident.  In the last year of the Civil War, ironclads were heavily used by both sides.  They mounted multiple cannons and were heavily armored.  As  shallow-draft gunboats, they could come close to shore or other ships and blast away almost with impunity. 

The Confederate ironclad ram CSS Tennessee in 1864 was the most powerful and dangerous warship in either navy.  At the Battle of Mobile Bay, it inflicted tremendous damage on Admiral Farragut's Union fleet.  The Tennessee finally surrendered after being surrounded by Union ships, rammed repeatedly by Union ironclads and pounded by broadsides at point blank range.  The Union repaired it and quickly put it back in action as the USS Tennessee.  It continued fighting until the end of the war after which it was sold for scrap. 

Land-based attacks were also more menacing since artillery now had the mobility to move with the front line assault troops and the power to inflict heavy damage.  The strategy of ringing a fort with modern cannon and pounding them into submission was used very effectively in the Civil War by both sides.

These advances and more brought an end to 1,000 years of fortress engineering, although the United States would continue to build, arm and man forts for another 80 years. It took the A-bomb to really convince the holdouts that forts were finished.

Interestingly, there were some forts that had no walls or defenses.  They were more like posts or towns than fortifications. One of them was Fort Bowie, the defender of Apache Pass in Arizona from 1862 to 1894. Despite being the center of a violent and protracted war against Cochise and the Apache for much of its life, the fort was laid out like a town and was almost totally undefended. It had running water, street lights and tennis courts.  It was never attacked by the Apache.

I hope you enjoyed this little primer on fort tactics.  As always, we welcome your comments via our email or our Guestbook.

Semper Fi .... Out here .... Alpha6