Historic California Posts, Camps, Stations and Airfields
History of the Coast Defenses of San Francisco and Significance of Battery Cavallo
by John A. Martini
Battery Cavello 1902: This view overlooking Battery Cavallo reveals the mounded earthen traverses typical of "Plan of 1870" works. Pairs of cannon would have been placed between the traverses. (Golden Gate National Recreation Area)

Spain, the first European nation to claim San Francisco, only half-heartedly defended the Bay. The tiny garrison at the Presidio was literally at the end of the empire, and resources were scarce. In 1794 they constructed a horseshoe-shaped adobe fort called "Castillo de San Joaquin" on a headland at the southern edge of the harbor entrance, primarily in response to a perceived British threat to California. Three years later, an even smaller battery called "Batteria San Jose" was constructed at the site of today's Fort Mason. Both fortifications quickly deteriorated in the wet, blowing weather of San Francisco.

The forts' condition declined even further under Mexican rule, and when America occupied San Francisco during the Mexican War the Castillo was in ruins and not a trace remained of the San Jose earthwork. As early as 1847, the Army's Corps of Topographical Engineers carried out surveys with an eye toward defensive positions around the harbor entrance.

By 1850, things had changed greatly. Gold had been discovered in 1848 on the American River, and within two years, San Francisco's population skyrocketed to nearly 40,000 people. The City was still a long way from nowhere, and strong defenses were critically needed. In November 1850 a joint Army-Navy board announced a sweeping plan for the defense of San Francisco harbor and all the Pacific Coast. The board recommended two large forts, at the entrance to San Francisco Bay, one on either shore of the straits that had recently become known as the "Golden Gate." This opening, only a mile across at its narrowest point, was a perfect defensive location for what the board referred to as the "outer line" of fortifications. The style of forts (or "works" as they were termed) envisioned were multi-tiered masonry forts of the type prevalent at harbor entrances and river mouths along the East Coast. A fort was planned for each side of the strait: one at "Fort Point" in the Presidio and one at "Lime Point" on the Marin shore. These forts would together mount nearly three hundred guns at the Gate's narrowest point.

Should any vessel be able to pass through their crossfire, an additional work was called for on Alcatraz where batteries at each end of the island could control the main shipping channels of the inner harbor. Finally, the Board recommended smaller backup batteries for Angel Island, Yerba Buena Island and Point San Jose. Guns at these points could intersect with the batteries of Alcatraz.

The Americans commenced construction in 1853 on the forts at Fort Point and Alcatraz. At Fort Point, the planned work was a three-tier masonry and brick fort at the site of the Spanish Castillo. Fort Point, as the new fort was called, was completed in 1861 and armed with a mix of heavy, smoothbore guns ranging in caliber from 24-pdrs. up through 10-inch Columbiads - the largest armament of the day. In the following four decades there were many changes in its armament, until the last guns were removed in 1900.

Simultaneous with construction of Fort Point, the Engineers undertook fortification of Alcatraz Island. Here, defenses involved construction of barbette batteries, masonry defensive walls, a fortified barracks called "the Citadel," a dockside brick and masonry casemate, a fortified sally port with moat and drawbridge, and other features. These, like Fort Point, were designed as permanent works to defend the Bay by controlling its mouth, the Golden Gate Strait. Alcatraz was completed in 1859 and remained a fort until 1907.

Acquiring title to Fort Point and Alcatraz was not a problem for the Army. Those lands had been under control of the Spanish and Mexican governments, so title to them was cleanly assumed by the United States of America. Lime Point, however, was part of the sprawling Rancho Saucelito owned by Capt. William Antonio Richardson. He had received title from the Mexican government in 1837, and his claim to the land was confirmed in 1854. Before the fort at Lime Point could be commenced, the land would have to be acquired from Richardson -- either through purchase or condemnation.

The story of the Army's negotiations with Capt. Richardson and the successor owner of the Rancho, William Throckmorton, has been related many times in other history studies, probably nowhere better than in Erwin Thompson's Historic Resource Study: Forts Baker, Barry, Cronkhite. Suffice it to say it took sixteen years of negotiations, correspondence, condemnations, and behind the scene maneuverings before the United States finally acquired title to the land. On July 24, 1866, final purchase was made of the "Lime Point Military Reservation" consisting 1,898.66 acres stretching from the Golden Gate to Point Bonita. The cost was $125,000.

Work immediately began on the long-planned casemated work at Lime Point. This fort, had it been completed, would have mounted 109 cannon in a two-story structure similar to Fort Point across the Gate. The fortification's planned site would necessitate carving out a four-acre plateau at the very foot of the point, and Colonel George Mendell of the Corp of Engineers soon had workman tunneling and hacking away at the heights. Mendell estimate that it would require an excavation of 1,000,000 cubic yards for the fort's foundations. And it would be an expensive job. He projected the total cost of the work to be a staggering $3,000,000 - more than $3.1 billion in today's dollars.

Simultaneously, the U.S. Army's Board of Engineers was reviewing the country's existing fortifications, especially in light of lessons hard-won during the Civil War. At siege after siege, heavy masonry works had shown their vulnerability. Multi-tiered masonry forts such as Fort Pulaksi and Fort Sumter had proven themselves to be little more than oversized targets for artillerymen. The Army soon realized it needed to radically redesign all its present and future forts.

Proposals ranged from hanging metal plates on forts' exterior faces to replacing them entirely with rotating iron gun turrets. More conservative Engineers, however, studied Civil War battlefields where dirt earthworks had been extensively used. These improvised fortifications were simple to build, provided excellent protection against enemy fire, and had proven easy to maintain and repair. Earthworks, the Board decided, would become be the basis of the next generation of permanent American forts. In the words of historian E.R. Lewis, "Never again would forts be built in the storybook style as single structures housing large numbers of cannon. From this time on, a fort was a piece of real estate occupied by a number of dispersed individual batteries."

These new American fortifications would be low-rise affairs, extending only a dozen feet above grade when viewed from the sea. In order to provide maximum protection for the guns, the weapons would no longer be mounted in the long-unbroken lines of platforms built in the 1850s. Now the Army planned to emplace cannon in pairs, and each pair would be separated from its neighbors by artificial earth hills called "traverses." The traverses would protect against incoming enemy shells and limit any battle damage to, at most, two weapons at a time. Each traverse was also to house a powder magazine for ammunition storage. Brick-lined, arched tunnels through the earthworks permitted the safe movement of men and supplies during battles.

All of the existing fortifications around San Francisco were now considered obsolete, especially the works at Fort Point and Alcatraz. New plans would have to be drawn up for earthworks that conformed to the new guidelines. At Lime Point, Col. Mendell suspended excavations and ordered surveys carried out of the nearby hills. Five sites were eventually chosen along the Marin shore for earthwork barbettes: the summit of Lime Point Ridge; Gravelly Beach; Point Diablo, Point Bonita; and Point Cavallo near Yellow Bluff. The new batteries would mount 74 weapons including mortars, smoothbore guns, and large rifles.

Mendell also designed plans for the other harbor forts around the Bay. On the southern shore of the Golden Gate, a mile-long line of earthworks would snake along the hilltops east and west of Fort Point and supercede that casemated fort work. At Alcatraz, the exposed pre-Civil War barbettes were to be demolished and new earthworks built in their place. Additional works were proposed for Point San Jose, Angel Island and Yerba Buena. Work was underway at Lime Point, Fort Point and Alcatraz by the end of 1870.

Col. Mendell considered the Point Cavallo battery especially important. Guns mounted on this promontory would cover not only the Golden Gate but also the inner bay to intersect with batteries in the Presidio, Point San Jose, Alcatraz Island and Angel Island. Mendell stressed that guns on the planned battery's left flank could also cover the important anchorage off Saucelito in Richardson's Bay. In addition to the main battery, he recommended that a small, two-gun "outwork" be placed at the very tip of Point Cavallo to protect Horse Shoe Cove. Plans for the two works were submitted to the Board of Engineers on April 9, 1870. (The construction of Cavallo was not finally approved until 1872, though, the delays principally caused by design concerns for installing the pending King's Depressing Carriage. Instead, construction first began at Gravelly Beach just west of Lime Point.)

Mendell's design for Battery Cavallo evolved into a symmetrical earthen fort, roughly in the shape of a broad arrowhead. (See Figure 1.) A long traverse with magazines bisected the work into two equal parts, each with its own parade area. Smaller traverses separated each pair of guns. Two "communication tunnels" pierced the central traverse to connect the north and south portions of the battery. The colonel feared an enemy landing party at Horse Shoe Cove might try to storm the battery from the rear so he enclosed the work on its landward side with an earthen parapet wall. This wall was also a defensive position, complete with firing steps for riflemen and embrasures for small cannon that could provide flanking fire along the exterior faces. Battery Cavallo thus became a totally enclosed earthwork -- a unique design not replicated anywhere else in the country.

Figure 1. This 1872 plan clearly shows Cavallo's arrowhead shape. Gun positions are indicated by semi-circular platforms, and underground rooms and tunnels by dotted lines. Guns on the right flank faced the Presidio, while those on the left faced Angel Island and Alcatraz. (John A. Martini)

Cavallo was also to have had the most massive firepower of any battery on the Pacific Coast. Preliminary plans specified 12-inch rifles, 13-inch mortars, 15-inch smoothbore Rodman cannon, and three monstrous 20-inch Rodmans. These latter weapons, weighing nearly 100,000 pounds apiece, would be able to fire a 1,000-pound solid projectile over four miles. Eventually, Cavallo's armament was changed to reflect a more standardized armament of fourteen 15-inch and one 20-inch Rodmans in the main battery and two 15-inch guns the outwork. Six mortars would be placed in the flat parades, positioned to fire over the earthwork parapets.

Construction finally began in June 1872 with construction of a road to the site. By July 1873 Mendell had succeeded in constructing the two arched passageways through the central traverse. The powder magazines were almost completed. The surrounding parapets had taken a rough shape, and sodding had begun on the interior slopes. In his annual report for fiscal year 1874, Mendell reported the main work completed except for the continuing problems of breast-height walls and platforms. Six months later he was able to say the same about the two-gun outwork. In October 1874 he summarized the cost of the battery (excluding the outer work) as $107,825.17. Not surprisingly, the vast majority of the funds ($76,744) had been expended for labor.

This condition would reflect the highest level of activity at Cavallo, for in 1875 the Lime Point appropriation for the coming fiscal year amounted to only $20,000 for all Marin's works. A parsimonious Congress was having doubts about expending vast amounts on new fortifications, especially in light of rapidly evolving military technologies demonstrated in Europe during the Franco-Prussian War of 1870-1871.

Only minor work took place over the next year at Cavallo. Some additional sodding was carried out, ventilators were installed in the magazines, doors were hung on the magazine in the two-gun outwork, and the road from Lime Point was repaired. As elsewhere in the nation, fortification construction came to a halt on June 30, 1876. That year, Congress allocated only a very small annual sum (roughly $100,000 for the entire United States) for "Protection, Preservation and Repair" of fortifications. Indeed, so drastic was the cut back on construction expenditures that only one gun had been mounted in all of the Lime Point fortifications - a lonely 15-inch Rodman on a wooden platform at Gravelly Beach. Of the much-vaunted 20-inch Rodman guns, only two were ever manufactured and neither left the East Coast.

Lime Point and all of the unfinished fortifications were relegated to caretaker status for the next two decades. At Cavallo itself, the battery stood 95% complete and lacked mostly finishing touches such as the masonry platforms for the Rodman guns, parapet walls at the salient positions, and a sally port (only a rough gap existed in the rear wall). However, with little maintenance, all the works soon began to fall into disrepair. Mendell's annual reports became repetitious on the topic. For example, in 1878 he wrote: "The works and public property have been under the charge of keepers throughout the year. No construction was in progress, all operations being suspended for want of funds. No changes have taken place either in number of platforms or in armament."

Interestingly, Mendell reported the earthworks on Alcatraz to be in the best condition of any, primarily because of their unique situation on an island. Over at Lime Point things were different: "A little rodent called the Gopher is the worst enemy we have. He burrows in the parapets and destroys their shape and compactness." Poisoning them did not help because "recruits from outlying country come in." Gophers, apparently, had not yet learned to swim.

In 1886, Secretary of War William Endicott convened a board to review the sad state of the country's defenses. Their sweeping recommendations would result in a wholesale rebuilding of American fortifications. At Fort Baker construction began in the mid-1890s on new batteries atop Lime Point Ridge and at Gravelly Beach, destroying the unfinished earthworks at those locations. Elsewhere around San Francisco harbor - and around the country for that matter - "Endicott" era fortifications soon obliterated the "Plan of 1870" earthworks that occupied the same strategic locations. In 1890 the Engineers proposed emplacing five disappearing guns atop Cavallo, but this new battery was dropped from subsequent construction plans probably because its field of fire would have been too restricted. Battery Cavallo escaped the vast Endicott construction program unscathed.

The Spanish-American War of 1898 brought a flurry of rearmament to America's forts. Dozens of aging Rodman guns were quickly emplaced to deal with the overrated (and, by the end of the war, sunken) Spanish fleet. In San Francisco, the Army installed pairs of 8-inch rifled Rodman guns to protect underwater mine fields within the Bay. At Fort Baker, three 8-inch rifled Rodman guns on iron front pintle carriages were emplaced in Cavallo at positions #10, 11, and 13. All three weapons were on the left flank of the work, apparently situated so their fire would intersect with similar guns on Alcatraz, Fort Mason and Angel Island.)

An interesting alteration also occurred about this time when additional earth was piled up in front of all the traverses. Originally these traverses had all been built with roughly rectangular footprints, and the additional earth changed these outlines into mushroom-like shapes when viewed from overhead. (See Figure 2.) Interestingly, the carefully drawn Engineer maps do not reflect this remodeling, nor do any written records mention the work. It is speculated that the reconfiguration probably occurred around 1898 to give additional protection to the Rodmans from flanking fire.

Figure 2. Battery Cavallo from the air, October 1937. Sixty years after its completion, Cavallo is little-changed from its original plan. (Golden Gate National Recreation Area)

Construction took time, though, and the war was over before the guns were mounted. Little documentation has been found regarding these three weapons, and it is not known if the guns were ever fired, even for test purposes. It is believed they remained until about 1910, at which time they were probably salvaged along with most of the rest of the obsolete ordnance in the Bay's defenses.

Battery Cavallo remained in a technological backwater for the next several decades, its only changes being the addition of two ancillary structures for nearby Endicott batteries. These were a powerhouse in the south parade constructed in 1910 for batteries Duncan and Yates, and an open-topped concrete observation station for nearby Battery Yates, built in 1918 at the very tip of the earthwork. Neither structure caused any significant impact on the historic fabric of the battery.

Up through World War II the old traverses continued to serve as a central magazine facility for Fort Baker "for the purpose of storing Powder Charges and other miscellaneous Ordnance appurtenances." The continued use of Cavallo as a magazine explains why its earthworks were kept so clear of vegetation during this period. Considering the highly incendiary and explosive materials stored inside its traverses, any vegetation that might create fuel for a fire would have been quickly cut away. Cavallo's earthworks were kept pristine and mowed up through the end of World War II, probably by soldier "fatigue parties."

Fort Baker experienced a major increase in military activity following Pearl Harbor, and activity in and around Cavallo increased. Coast Artillery troops set up temporary antiaircraft guns and searchlights near the battery, upgraded the old Duncan-Yates powerhouse, and erected a machine gun position atop one of its earthen traverses, probably for a .50 caliber weapon. Cavallo's magazines probably also held TNT for the nearby mine depot.

The increased wartime activity within the old earthwork battery also led to physical alterations when a access road was bulldozed through its superior slope and into the battery at position #3. (Sometime after the war, a second road was bulldozed on the landward face of the battery to provide a bypass for vehicles too large to fit through the brick communication tunnels.)

Following the war, Cavallo entered another period of neglect. All ammunition stores were apparently removed about this time, and vegetation began to encroach onto the carefully graded earthworks, obliterating their form and confusing their original function. Army documents and maps over the next thirty years show the battery designated a "storage and training" area although one 1968 map states that the two curved magazines flanking position #8 were again being used for explosive storage, "but not more than 100 pounds total for both." The same map also indicates that the magazines all still retained their original 4-inch thick wooden doors.

Battery Cavallo today remains remarkably intact under a cover of coastal scrub. The only alterations to its historic 1870s earthworks are relatively minor: the 1918 range-finding station for Battery Yates, the two vehicle roads constructed through the earthworks, and the sandbag-lined machine gun emplacement atop a traverse. No traces remain of the Duncan-Yates powerhouse, demolished in the 1970s. (See Figure 3.) Internally, the structure has been altered by the removal of the wooden doors from the traverse magazines and by the demolition of interior "cross walls" within the magazines. These walls, designed to prevent wayward cannonballs from entering the powder storage spaces, were probably removed to facilitate moving ordnance stores in and out of the magazines. Lately, the brick communication tunnels have become the targets of graffiti "taggers," some of who have created spray can murals stretching more than thirty feet.

Figure 3. Battery Cavello circa 1941. The Fort Baker Station Hosital is in the foreground.

Military fortification historians agree that Battery Cavallo is an outstanding example of "Plan of 1870" fortifications. In his landmark Historic Resource Study: Seacoast Fortifications San Francisco Harbor, Historian Erwin Thompson wrote, " Of all the works constructed in the 1870s, the Cavallo Battery was the most handsome architecturally and is the best surviving example of the post-Civil War earthworks . . .. It is recommended that the necessary restoration of the parapets be carried out and that the battery be preserved and interpreted as a prime exhibit of the post-Civil War modernization project." Recently Dr. Matthew Adams of the Coastal Defense Study Group added his opinion: "Cavallo remains to my mind the only 'fort' style 1870s construction built as part of the post-Civil War program and not as a detached outwork to some already existing brick fort. [It is] architecturally unique."

This originally appeared in the Park News, published by the Golden Gate National Parks Conservancy. Republished with permission of the author.
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