San Diego Once Planted 15 Explosive Mines in Its Harbor
During the Spanish-American War in 1898, the U.S. Army planted 15 electrically controlled explosive mines across the entrance to San Diego Bay. Here's the forgotten story of the harbor's underwater defenses.
Greg Ross
CEO / Owner - Nancy's Vacation Rentals
SAN DIEGO UNCOVERED
San Diego Once Planted 15 Explosive Mines in Its HarborImagine sailing toward San Diego Bay and discovering that the channel ahead had been deliberately filled with explosives.
Not during World War II.
Not during the Cold War.
In 1898.
As the United States went to war with Spain, the U.S. Army planted 15 electrically controlled mines across the entrance to San Diego Bay.
They weren't drifting explosives. They were part of a sophisticated coastal-defense system controlled from shore.
First, About the Word “Submarine”
Historical Army records call these weapons submarine mines.
That does not mean submarines planted them, and it does not mean they were designed specifically to attack submarines.
In nineteenth-century military terminology, “submarine” simply meant underwater.
These were submerged explosive charges—what we would now recognize as controlled naval mines.
Why Was San Diego Mining Its Own Harbor?
The answer begins with the Spanish-American War.
On February 15, 1898, the battleship USS Maine exploded in Havana Harbor. The disaster intensified tensions between the United States and Spain, and war followed in April.
American military planners suddenly had to consider whether strategically important ports on both coasts were adequately defended.
San Diego was not yet the enormous Navy city it would become, but its deep-water harbor and position near the Mexican border made it strategically important.
The Army Had Already Been Preparing
The harbor minefield wasn't improvised from scratch after war began.
During the 1880s and 1890s, the United States had been modernizing coastal defenses under what became known as the Endicott system.
At Point Loma, engineers were already building new gun batteries and infrastructure near Ballast Point.
In 1897—before the Spanish-American War—the Army constructed a bombproof mining casemate near the future Battery Wilkeson.
That underground control room would become the nerve center of San Diego's underwater defenses.
The Mines Were Wired to Shore
The system was remarkably advanced for the 1890s.
Electrical cables ran from the minefield underwater back to the protected casemate on shore.
From there, Army personnel could monitor and control the explosives.
The mines could be detonated electrically when an enemy vessel entered the appropriate area.
In other words, this wasn't simply a field of explosives waiting for any ship to hit them.
It was a remotely controlled harbor-defense system.
Then Came an Unusual Order: Find 120 “Patriotic Citizens”
When war began, Lieutenant George H. Meyler received orders to mine the entrance to San Diego Bay.
The instructions came with an extraordinary requirement: recruit a corps of 120 patriotic citizens to help do it.
Meyler didn't quite reach 120.
He assembled about 80 civilian volunteers.
Who Volunteers to Plant Explosives?
The volunteer force wasn't random.
Historical National Park Service research lists electricians, civil engineers, surveyors, telegraphers, boilermakers, steam engineers, mechanics, carpenters, divers and laborers.
These were people whose technical skills could actually help construct an electrically controlled underwater minefield.
Still, willingness wasn't the same as experience.
The Professionals Had to Step In
Cable, explosives and other supplies arrived by steamer from San Francisco.
On May 11, five enlisted Army engineers experienced in mine laying arrived in San Diego.
Army accounts noted that the civilian volunteers were enthusiastic but inexperienced, sometimes causing delays.
The five trained soldiers helped load the explosive “mine torpedoes” and supervised the volunteers' work.
Fifteen Mines Went Into the Channel
Eventually Meyler's team succeeded.
Fifteen electrically controlled mines were planted in the entrance channel to San Diego Bay.
But the Army couldn't simply close the harbor.
A safe passage was deliberately left open so friendly commercial vessels could continue entering and leaving San Diego.
So How Did Friendly Ships Get Through?
The minefield was part of a controlled defense zone rather than an indiscriminate barrier.
Authorized traffic could use the safe channel.
If an enemy ship attempted to force its way through the defended entrance, personnel ashore could use the mine system in conjunction with coastal artillery.
The concept was simple: funnel hostile ships into predictable water and then attack them from both above and below the surface.
The Army Put Guns Over the Minefield Too
Two older smoothbore cannon protected the minefield during the 1898 emergency.
The broader Point Loma defense system was simultaneously becoming far more formidable.
Battery Wilkeson, completed in 1898, mounted four 10-inch disappearing rifles. Additional batteries followed around the entrance to the bay.
The underwater mines were therefore only one layer of a developing defensive network.
What Was a “Disappearing” Gun?
The term sounds like a magic trick, but it describes a clever artillery system.
A large coastal gun could remain protected behind a concrete parapet while being loaded.
When ready to fire, the carriage raised the weapon above the wall. After firing, recoil helped return it to its protected position.
Combined with underwater mines, smaller rapid-fire guns and observation stations, these batteries were designed to make San Diego Bay extremely difficult for an enemy fleet to enter.
Was a Spanish Fleet Really Coming?
No attack materialized.
National Park Service research goes further, noting that there was effectively no danger of a Spanish attack on San Diego Harbor.
But military planners in the opening weeks of a war could not simply assume that.
The minefield reflected the uncertainty and anxiety sweeping American coastal cities in 1898.
The Mines Stayed in the Water for Months
Even after the immediate fear subsided, the mines remained planted through the summer.
They were finally removed in September 1898.
San Diego's first wartime harbor minefield had existed for only a few months.
But the infrastructure and military thinking behind it were here to stay.
The Mine System Became Part of Fort Rosecrans
The coastal defenses at Point Loma soon acquired a familiar name.
In 1899, the War Department named the fortifications Fort Rosecrans, honoring Civil War general William Starke Rosecrans.
Over the following decades, Point Loma became increasingly covered with gun batteries, fire-control stations, searchlights and other military installations.
The 1898 minefield was an early glimpse of San Diego's future as one of America's most strategically important military harbors.
The Army Kept Using Underwater Mines
Controlled harbor mines did not disappear after 1898.
They became a standard part of American coastal-defense planning.
San Diego continued experimenting with them into the twentieth century. In 1914, Army and Navy aviators even flew over minefields near Fort Rosecrans to determine whether underwater mines could be spotted from aircraft.
On clear days and in clear water, observers discovered that some of them could.
Technology was already beginning to challenge technology.
Picture the Entrance to San Diego Bay in 1898
There was no modern downtown skyline.
No Coronado Bridge.
No giant Navy fleet lining the waterfront.
But beneath the water between Point Loma and the opposite side of the harbor entrance sat explosive charges connected by electrical cables to soldiers hidden inside a protected control room.
And above them stood artillery intended to finish whatever the mines started.
San Diego Was Becoming a Military City
The story matters because 1898 sits near the beginning of a transformation.
For much of the nineteenth century, San Diego's harbor had been associated with hide trading, whaling, fishing and commercial shipping.
By the twentieth century, military installations would become one of the defining features of the region.
The minefield at Ballast Point was a sign that Washington increasingly viewed San Diego Bay not simply as a port—but as a strategic asset worth defending.
And Yes, San Diego Really Mined Its Own Harbor
The headline sounds like something from World War II.
But in 1898, San Diego really did place explosive mines beneath the entrance to its own bay.
Fifteen of them.
Electrically controlled.
Installed with help from roughly 80 local civilian volunteers.
And kept ready for a Spanish attack that never came.
San Diego Uncovered
San Diego Uncovered explores the forgotten defenses, strange decisions, lost places and unexpected stories behind America's Finest City.
The next time you look across the calm water at the entrance to San Diego Bay, remember:
there was once an electrically controlled minefield underneath it.
Explore San Diego With Nancy's
Nancy's Vacation Rentals has been helping guests experience San Diego for more than 25 years. We love sharing the stories behind the coastline, neighborhoods and landmarks that make San Diego unlike anywhere else.
Browse Nancy's San Diego Vacation Rentals
Sources & Further Reading
Keep reading
How a Polynesian Voyaging Canoe Helped Create America's Largest Pacific Islander Festival
Right Here in San Diego
Why Is There an Oktoberfest in El Cajon?
The 200-Year Journey From Bavaria to San Diego
What Happens to Your Airbnb Listing When You Change Property Managers?
Changing vacation rental managers? Learn what can happen to your Airbnb listing, reviews, reservations, photos, pricing, co-host access and guest communication during the transition.