California State Military Department
The California State Military Museum
Preserving California's Military Heritage
Historic California Posts, Stations and Airfields
San Francisco Defense Area Site SF-25 (Rocky Ridge)
(Mount Martell Air National Guard Radio Relay Site)
by Daniel M. Sebby
Command Sergeant Major
California Center for Military History

The San Francisco Defense Area Site SF-25 was perhaps the shortest lived “permanent” installation in ring of Nike sites that defended the San Francisco Bay area. Activated in 1956, the site was deactivated three years later. The site was armed with the Western Electric SAM-A-7/M1/MIM-3 Nike-Ajax through out its short history. A detailed history of this system in included in paragraph, below.

The U.S. Army’s Cold War antiaircraft/air defense artillery sites were identified by an identification system that included the initial(s) of the defense area and a site number (i.e. SF-25 meaning San Francisco Defense Area Site 25). To this basic identifier was a suffix identifying the function of the site or portions of the site. These would have included suffixes for gun and missile batteries, command and control facilities, and administrative and family housing areas.

When dealing with Nike sites, the overall site was identified by the basic identifier with three distinct functional areas identified by the suffixes A, C, and L:

Administrative Area (SF-25A): The Administrative Area contained the site’s administrative and support functions. Normally, this would have included troop housing and messing, recreational facilities, battery administration and supply buildings, and vehicle maintenance facilities. The site was considered so remote at the time that the U.S. Army built family housing within the Administrative Area to house up to twelve families of the garrison’s married noncommissioned and commissioned officers. This was unique to the batteries of the San Francisco Defense Area as most of the other sites were either on Army installations or in urban/suburban communities. This area was competed one year prior to the site was deactivated.

Control Area (SF-25C): The Control Area (also known as the Integrated Fire Control or “IFC” area) was the location of the battery’s radar and fire control systems. The IFC area was located at a site on Mount Martell that allowed for 360º “line of site” radar coverage by the battery’s missile and target tracking and search radar systems. The reason for locating the site away from the launch area was that the missile tracking radar would “lock on” to the missiles while they sat on the launcher and followed them from launch to impact with the target. The high speed of the Nike family of missiles would have destroyed the tracking mechanisms of the missile tracking radar if they were located close to the launchers.

Launch Area (SF-25L): Normally located adjacent to the administrative area, the Launch Area consisted of the missile launchers and magazines (underground storage “bunkers”) as well as missile and warhead assembly, maintenance and fueling facilities. As such, this was the most secure area of the site and also included a ready room for missile crews when the battery was in a “hot” or ready status, security checkpoints and a kennel for military working dogs.

Site SF-25 was initially garrisoned by Battery B, 441st Antiaircraft Artillery Missile Battalion. With the implementation of the U.S. Army’s Combat Arms Regimental System (CARS), this unit was redesignated Battery B, 4th Missile Battalion, 67th Artillery. The battery was inactivated concurrent with the site’s deactivation in July of 1959.

San Francisco Defense Area Site SF-25, less the Control Area, was reported as excess to the General Services Administration who began disposing of the site.

Despite the ending of the air defense mission and the deactivation of the Launch and Administrative Areas, the Control Area atop Mount Martell had a much longer military history. This site was initially leased from the East Bay Municipal Utility District (EBMUD) in 1955, with a new lease negotiated in 1960. In 1962, the site was transferred from the U.S. Army to the U.S. Air Force for use as a radio relay site under the control of the California Air National Guard’s (Cal ANG) 234th Combat Communications Squadron located at Hayward Air National Guard Station. It was during this time that the former Control Area was known a Mount Martell Air National Guard Radio Relay Site.

With changes in technology and missions, The Cal ANG no longer required the entire site after 1966 and the lease was terminated and replaced by a license and access permit allowing the Cal ANG to mount relay equipment on existing poles and antenna structures. This relationship with EBMUD continued until 1984 when the Cal ANG withdrew from the site and terminated all agreements.


The Western Electric SAM-A-7/M1/MIM-3 Nike Ajax

The Nike Ajax was the world's first operational surface-to-air guided missile system. Its origins lay in the immediate post-war time, when the U.S. Army realized that guided missiles were the only way to provide air-defense against future fast high-flying bombers. Western Electric became the prime contractor for the XSAM-G-7 Nike missile system and Douglas as the primary subcontractor was responsible for the missile airframe.

The first unguided Nike missiles were fired in 1946, but problems with the original multi-rocket booster (eight solid-fuel rockets wrapped around the missile tail) soon led to delays in the program. In 1948, it was decided to replace this booster pack with a single rocket booster, attached to the back of the missile. The main propulsion of the missile was a Bell liquid-fueled rocket motor, and the flight path was controlled by the four small fins around the nose. In November 1951, the first successful interception of a QB-17 target drone succeeded. The first production Nike (which had been redesignated SAM-A-7 in 1951) flew in 1952, and the first operational Nike site was activated in 1954. By this time, the missile had been designated by the Army as Guided Missile, Anti-Aircraft M1. The name had changed to Nike I, to distinguish it from the Nike-B (later MIM-14 Nike Hercules) and Nike II (later LIM-49 Nike Zeus). On 15 November 1956, the name was finally changed to Nike Ajax.

The Nike Ajax missile used a command guidance system. An acquisition radar called LOPAR (Low-Power Acquisition Radar) picked up potential targets at long range, and the information on hostile targets was then transferred to the Target Tracking Radar (TTR). An adjacent Missile Tracking Radar (MTR) tracked the flight path of the Nike Ajax missile. Using tracking data of the TTR and MTR, a computer calculated the interception trajectory, and sent appropriate course correction commands to the missile. The three high-explosive fragmentation warheads of the missile (in nose, center, and aft section) were detonated by ground command, when the paths of target and missile met.

One of the major disadvantages of the Nike Ajax system was that the guidance system could handle only one target at a time. Additionally, there was originally no data link between different Nike Ajax sites, which could lead to several sites engaging the same target. The latter problem was eventually solved by the introduction of the Martin AN/FSG-1 Missile Master command-and-control system, with automatic data communication and processing. Other problematic features of the Nike Ajax system were the liquid-fuel rocket motor with its highly toxic propellants, and the large size of a complete site with all components, which made Nike Ajax to all intents and purposes a fixed-site air defense system.

By 1958, nearly 200 Nike Ajax sites had been activated in the United States. However, the far more advanced MIM-14 Nike Hercules soon replaced the Nike Ajax, and by late 1963, the last Nike Ajax on U.S. soil had been retired. In 1963, the Nike Ajax had received the new designation MIM-3A. Despite the use of an MIM (Mobile Intercept Missile) designator, the mobility of the Nike Ajax system was more theoretical than actually feasible in a combat situation.

The MIM-3A continued to serve with U.S. overseas and friendly forces for many more years. In total, more than 16,000 missiles were built.

Source: Directory of U.S. Missiles and Rockets,





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