Coastal defenses are often thought of as something only found in Europe, such as on Germany’s famous Atlantic Wall. So you may be surprised to learn that the US, a country that famously came away from the Second World War unscathed, actually has a significant amount of coastal defenses, some of which were even armed with battleship guns!

A great example of this is the defenses just outside the west coast city of San Francisco, straddling the Golden Gate entrance to the harbour.

Here, a number of large caliber gun batteries were built in the first half of the 19th century, with large-scale construction of many bunkers, observation posts, radar facilities, and even Cold War air-defence rockets.

San Francisco Defenses

The up-gunning of the United States’ coasts began in the late 1800s, when the US was in the early days of the becoming the formidable superpower that we know today. The Endicott Board, established in 1885, sought to gain a better understanding of the nation’s defenses and their effectiveness.

The board found it was undersized, understrength and severely outdated. Thus, a large construction project began to modernise and update them. It is important to remember that the aircraft is still over a 15 years away, so if any nation other than Mexico or Canada wanted to take the US, they had to come by sea.

The most vulnerable and strategically important areas of the coast were identified and prioritised for reinforcement. San Francisco, with its large, natural harbor, was deemed one of the most vital coastal areas to protect.

Fortunately, anyone planning on entering San Francisco’s harbor must past through the Golden Gate, a strait around one mile wide at its thinnest point. For a defender this is ideal, as it allows you to hit the intruder on both sides.

In 1900 the US government acquired a patch of land south of the Golden Gate that was perfectly suited to guard this entrance. This would become Fort Funston. However, construction of defenses here would not begin until the First World War.

A second site, Fort Cronkhite, began construction in the latter half of the 1930s. This site was located on the north side of the Golden Gate, opposite Fort Funston.

But before the decade was up these sites became home to some of the most powerful weapons in the world: 16-inch guns. Guns of this size and caliber had long been desired, as battleships would need to stay far away to keep out of their range.

The Army had developed a massively powerful gun of this size, the 16-inch/50-caliber M1919, but it was so big and expensive that large only a handful were built.

Their luck would change in the late 1920s though, when they began receiving 16-inch guns from the US Navy.

One Man’s Trash, Another Man’s Golden Gate Defense

Back in the First World War, the US Navy had commissioned the construction of two classes of ships – South Dakota-class battleships and Lexington-class battlecruisers – that were to be armed with new 16 inch guns.

These guns were the 16-inch/50-caliber Mark 2, and they were some of the most powerful in the world. Each 130-ton, 21 meters (68 feet) long gun was capable of lobbing a one-ton round out to a range of 25.5 miles (41 km).

70 guns were built to arm these ships, but in 1922 both classes were suddenly cancelled as part of the Washington Naval Treaty.

So without any ships to put them on, the 16-inch/50-caliber guns were placed into storage with the hope of fitting them to ships one day. In the 1920s the Navy began making them available to the US Army, the branch responsible for manning coastal defenses.

The Army, having been wanting 16-inch guns for a while, quickly began planning how they would use them their own forts, including those outside of San Francisco.

This was settled in the late 1930s, and so two new gun batteries began construction to house them; Battery Davis at Fort Funston, and Battery Townsley at Fort Cronkhite.

Battery Davis

Battery Davis was the first of the two to begin construction, starting in November 1936. Engineers had factored in the increasing threat of aircraft, and decided to place the guns under concrete and earth inside casemates.

Two casemates (a fortified structure housing a gun) were built, with each containing one 16-inch gun. This was the first time such a structure had been built for a gun of this size in the US, and it was important to get it right as it was going to be the blueprint for the others that followed.

The guns were first placed on their platforms 600 feet apart, and then immense concrete structures were built over them. The roofs were up to 4 meters thick of single-poured, steel reinforced concrete.

Above the casemate, seperated by layers of sand and earth, was a second layer of concrete 600 mm thick. On top of this was more earth.

This “burster” layer was added to detonate bombs or rounds before they reached the actual bunker roof.

The two gun casemates were connected via a large corridor, complete with tracks and hoists to move the one-ton 16-inch rounds from the storage rooms to the guns. A system borrowed from naval vessels removed gasses after firing.

Construction was complete by early 1939, and the battery was handed over to the Army who began training crews.

Battery Townsley

Meanwhile, work on a battery over at Fort Cronkhite had began in 1938, named Battery Townsley. It benefited from coming after Fort Davis, as engineers and construction teams were able to incorporate and apply lessons that had been learned.

Battery Townsley had two 16-inch guns like its sibling, mounted casemates 350 feet apart. In general, the two batteries were very similar and built to the same standards.

This included both having their own dedicated power supply to ensure they wouldn’t suddenly be cut off during battle.

But Battery Townsley also had its own reserve ammunition storage nearby due to its isolation. On the other hand, Battery Davis’ reserve ammunition supply was located at a pre-existing installation south of the Golden Gate.

Sat 350 feet high on Wolf Ridge, Battery Townsley had a commanding position above the harbor.

16-inch Gun Battery Service

Despite Battery Davis being completed first, it was actually Battery Townsley that would fire its guns first. This occurred on July 1, 1940, marking the first time a 16-gun gun was fired on the United States’ west coast.

Following this, the batteries’ crews drilled over and over to ensure that the guns could be used whenever an enemy may arrive. At Fort Townsley, the gun crew actually slept in the bunker as the gun had to be ready to fire in just 15 minutes.

Thanks to the range and traverse of the guns, they were able to cover an immense area outside San Francisco harbor. Test firings revealed that the guns had a range of 25-26 miles, enough to hit the Farallon Islands.

The importance of the two 16-inch gun batteries suddenly increased after Japan’s attacks on Pearl Harbor in late 1941. There was now a very real threat to the US’ west coast, but the batteries ensured that anyone who tried to take San Francisco had to stay 25 miles off the coast to be safe.

Their guns were capable of holding even modern battleships at long range if they wish to avoid being hit, so they were very important for as long as the Japanese threat lasted.

Regular test firings took place, with Battery Townsley firing around 200 rounds from its two guns over its service.

Targeting and corrections were made by a network of observation bunkers positioned along the coast north and south of the forts. Spotters would visually watch for targets, and if they were engaged, would provide corrections to the big guns’ fire.

The most famous of these is the Devil’s Slide bunker. Today, this large structure sits precariously on top of a mount on the edge of jagged cliffs.

Sometime in 1943/1944, the forts received a revolutionary new piece of technology; radar. These sets, SCR-296s, could accurately detect and range-in targets up to 90 km away, far more than any human observer could track.

But they weren’t only accurate, they could be used at night, and in rain and fog. This greatly increased the batteries’ capabilities.

Abandonment

As the war in the Pacific progressed, it became clear that Japan would not be able to launch any significant attack on the west coast of the US.

As a result the importance of Battery Davis and Townsley reduced. Before the war had even ended parts of the sites were already being used for storage and training.

In 1948, with the war now over and more advanced coastal-defense systems around the corner, the guns were cut up for scrap and the batteries became inactive.

That wasn’t the end for these great forts though, as in 1955 they were suddenly given a new lease of life. This was thanks to the installation of Nike missiles.

Nike missiles were a post-war missile developed to counter the threat of incoming Soviet bombers. The first type was the Nike Ajax, but these were replaced by the nuclear-tipped Nike Hercules.

Launcher sites, along with their control centers and support staff, were constructed at Fort Funston and Fort Cronkhite. These would remain in service until 1965.

Today both forts are under the administration of the National Park Service, and the big 16-inch gun casemates of Fort Davis and Fort Townsley are still there and possible to visit.