With input from Ken Glaze

Ever wonder about Cabrillo National Monument’s bunker? The one located between the main parking lot and the lighthouse?

What is commonly called the “bunker” at CNM is more accurately named the “Battery Command and Base End Station, Battery Ashburn” and is one of 21 military structures within the monument’s boundaries.

The Point Loma peninsula forms a natural protective barrier at the entrance to San Diego Bay, rising 422 feet to provide strategic views of the harbor and ocean. In 1852, the government of the United States designated the area as a military reserve. 

In 1899, the War Department dedicated Fort Rosecrans and began building a series of gun batteries. Between 1918 and 1943, the Army constructed searchlight bunkers, base end stations and gun batteries on the site. During World War I and World War II, military facilities in Point Loma provided vital coastal and harbor defense systems.

A base end station is one of a pair of stations at either end of a precisely measured (surveyed) baseline. During wartime, once simultaneous bearings from each base end station to a target were taken, since the distance between the stations (the baseline) was known, the range to the target from either station could be calculated through triangulation. If the target’s bearing from each station was sent to a plotting room and input to a plotting board, the position of the target could be estimated and firing coordinates for a gun battery could be calculated.

Battery Ashburn was built in 1943, and the base end station (bunker) was where the officer in charge of Battery Ashburn worked. This station/bunker also served as the primary observation post for the Battery. Other components of the Battery included: observation posts, plotting and switchboard rooms, command stations, motor generator rooms, storerooms, shell and powder rooms, latrines, and equipment rooms. Since Battery Ashburn featured the biggest guns mounted in Point Loma, this station/bunker was an important part of the strategic defense of San Diego. It supported the Battery’s two 16-inch diameter guns, which could fire 2,300-pound shells nearly 30 miles out to sea. 

To say that these guns were massive is an understatement. Look at the size of the guns in relation to the people in the photos.

There were six base end stations (bunkers) for Battery Ashburn (BC3), however there were never more than three active base stations at any given time. They were defined by the following nomenclature: B = target azimuth station. S = shot/splash azimuth station. The numbers added to the “B” and “S” designators were the “Tactical Number” of the battery. This was the number assigned to each battery by Fort Rosecrans so each battery could be quickly identified. It should be pointed out the classification of the various base stations for Fort Rosecrans is not well documented.

Battery Ashburn was one of five batteries for Fort Rosecrans: #1 was Battery Woodward, #2 was Battery Strong, #3 was Battery Ashburn, #4 was Battery Cabrillo, and #5 was Battery Humphreys.

The structure for the bunker at Cabrillo is referred to as the North Fort Rosecrans structure (B1/3) (S1/3).

The commander of 16-inch-gun Battery Ashburn operated from the bunker located at Cabrillo. On the top level (BC3) he directed the firing of the guns. The lower level (B1/3 S1/3) served as one of the five base end stations (bunkers) for Battery Ashburn. The roofs were camouflaged to resemble large rocks. Steel rings on the roofs served as anchors for camouflage netting. The steel shutters that protected the observation slits still remain. An exterior flight of concrete steps leads to the lower level. 

During World War II, Cabrillo National Monument was closed to the public and was not
reopened to visitors until November 11, 1946.

The bunker/base end station was part of the Coast Artillery Corps (CAC). The CAC was a part of the Army in the same way that the Marine Corps is a part of the Navy. The CAC was assigned to defend American harbors from attacks by hostile warships using a series of forts mounting a variety of large, medium and small guns. Just before WWII the War Department decided to modernize the CAC by building state-of-the-art facilities consisting of new gun emplacements, observation stations and support structures. Our bunker is one of those structures.

The bunker remained active until 1945 and the end of WWII, when the War Department decided the idea of coastal artillery forts was obsolete. The guns were dismantled and sold for scrap, the CAC was dissolved, and the forts were abandoned. 

In our case, the bunker was part of the area returned to the National Park Service in 1947, and NPS converted the bunker into an office. It was used as an office, darkroom, and storage area until it was abandoned in 1967, when the current Visitor Center was completed. At that time, the decision was made to concentrate on restoring the natural environment rather than the abandoned military structures.

Howard Overton became a ranger at CNM in 1977 and was assigned to be chief of resources management and visitor protection. Part of that job was to understand the history of the area, so he started to study the history of Fort Rosecrans. At the same time another ranger, Brett Jones, started contacting WWII veterans to arrange interviews with them and to attend veteran reunions. Overton managed and performed the veteran interviews and eventually collected them into a book called “19th Coast Artillery and Point Loma Remembrances” that was first published in 1993. That is the book Ken Glaze, Cabrillo’s lead volunteer WWII historian, restored. Overton eventually became CNM’s superintendent before retiring from NPS in 1994.

Nothing further happened until 1999, when NPS performed a survey of the military structures at CNM. The survey coincided with an attempt to conserve the structures that showed the worst age-related damage. CNM also recognized the importance of Fort Rosecrans to the cultural history of the area and installed the Coast Artillery Museum that currently resides in the radio room structure near the bunker and parking area.

As part of that survey report, a summary of the condition of the structure stated the following:

BATTERY COMMANDER AND BASE-END STATION, BATTERY ASHBURN: RESTORATION [2]

Note: Painting occurred in early 1998 and was in progress during field work for this report. We do not know the extent of testing, cleaning and preparation that occurred prior to this work, nor do we know the authenticity of the selected colors. We suggest monitoring this structure for signs of recurring cracking, spalling and corrosion.

• Repair concrete spalls, with special attention to door header. Cut out and replace or treat existing reinforcing rod at this location as needed.
• Repair cracks in concrete.
• Replace metal pipe railing in-kind.
• Remove rust from all metal elements, abating or encapsulation lead paint. Treat with rust inhibitor, and paint with approved historic colors. Recent painting of metal shutters did not remove rust.
• Remove plywood infill at exterior door and replace metal vents at upper and lower openings.
• Replace strip fluorescent fixtures with historically appropriate incandescent (probably bare lightbulb and plain socket).
• Remove peeling paint from floors.
• Replicate and install missing camouflage netting. Netting to be attached to extant eyebolts at roof.
• Review roof slab drainage. Create swales to redirect any surface runoff.
• Remove efflorescence and conduct repairs at exterior door soffit.
• Restore function to metal shutters by removing wood and clamps. Repair or replace in-kind window shutter hardware.
• Straighten bent metal shutters at lower level.
• Replicate and replace removed chart shelf.
• Replicate and replace missing window shelf.
• Remove brick rubble from lower room.
• Reopen electrical raceways between lower rooms.
• Replicate missing metal door frame to match adjacent galvanized metal.

In 2004, Secretary of the Interior Gale Norton visited Cabrillo as part of her Earth Day tour. Her visit included a tour of the bunker as seen in this photo (talking with Superintendent Terry Dimattio). 

The structure remained untouched until 2010, when Tom Workman, then park superintendent, decided to allow volunteers to start restoring the bunker. These images show the bunker as it looked in 2012 when it was reopened. 

The work Cabrillo’s Military History volunteers did in the Battery Ashburn command bunker involved cleaning it out, repainting it to match the tan color found in other bunkers, and restoring the stenciling and equipment that was original to the bunker. The goal is to have the bunker appear, as close as possible, to how it looked when it first opened in 1943. Future plans include cleaning out, but not restoring, the bunkers near the Kelp Forest (Whale Watch) Overlook and the statue of Cabrillo. Unlike the command bunker, these bunkers were never modified by NPS, so the intent is to make them presentable for special tours, but to otherwise leave them in their current state.

All the equipment inside the bunker is accurate to the time period and was researched and collected by the volunteer restoration crew. 

Here are some photos of how the Bunker looks today.

To get a more in-depth description of the bunker/base end station and learn more about its various functions, go to the ebinder document A Brief History of Fort Rosecrans.

Take a photographic tour of the bunker in the ebinder document “Photographic Tour Of The Base End Station At Cabrillo National Monument“.   

The bunker is open for visitation every Saturday from 9:00 a.m. to 2:30 p.m., as CDC and county restrictions allow.

References

Wikipedia – https://en.wikipedia.org/wiki/Base_end_station

Historic Structures Report – http://www.npshistory.com/publications/cabr/hsr/contents.htm

http://www.militarymuseum.org/BtyAshburn.html

http://www.npshistory.com/publications/cabr/guns-san-diego-hrs/chap7.htm

Last revised 10-Aug-21