Historic Posts, Camps, Stations and Airfields
San Francisco Defense Area Antiaircraft Artillery Site 40
(Naval Radio Station, South San Francisco)
History (2007) by Dan Sebby
Prior to military or naval use, the site was a radio transmitter site operated by Federal Telegraph Company from 1912 until 1925 when the station was sold to MacKay Radio and Telegraph Company. The station provided radiotelegraph service to ships operating between San Francisco and Hawaii. This activity gave the site the name “Radio Hill” (http://www.sfmuseum.org/hist/poulsen.html).
The first reference to Navy usage of the site was a single map in the US Army Corps of Engineers, Sacramento District real estate file showing the Site as a U.S. Naval Radio Station. Further research indicated that the U.S. Navy operated a dadio direction finging station known as Naval Radio Station South San Francisco from when it was transferred from the Farallon Islands in June 1942 and until it was relocated to Castroville in March 1943. Research has not found the means in which the U.S. Navy obtained and disposed of the Site during their period of control.
Southern Pacific Company Map of Former San Francisco AAA Battery 40

With the start of the Korean War on 25 June 1950, the possibility of an attack by long range manned bombers of the then Soviet Union caused the U.S. Army reestablish a system of antiaircraft defenses. The U.S. Army was in the middle of the development of the Nike-Ajax antiaircraft missile at that time (Moeller 1995).
This required the U.S. Army rely on World War II-era 90mm and 120mm mobile antiaircraft guns until the Nike-Ajax missile were put into operational service. The Korean War also created a shortage of U.S. Army anti-aircraft artillery battalion to defend the United States (Moeller 1995).

Typical 90mm Antiaircraft Artillery Gun Battery
With this in mind, when the U.S. Army obtained the Site on 8 September 1951, it was garrisoned by a battery from the California Army National Guard’s 250th Antiaircraft Artillery Group. This unit and its two battalions were ordered to Federal service on 15 May 1951. Research has not determined a specific battery or battalion that garrisoned the Site (Thompson 1997).
Each firing battery had four towed 90mm guns plus fire direction equipment. This would consist of the M1 or M2 90mm antiaircraft gun, the SCR-584 microwave tracking radar in a trailer, the M-9 or M-10 gun director system in a second trailer, and supporting equipment such as trailer or skid-mounted generators.
On 14 May 1953, the garrisoning battery was released from Federal service and returned to state control at its home station at the San Francisco Mission Street Armory. It was replaced by Battery D, 271st Antiaircraft Artillery Gun Battalion, California Army National Guard (California Military Department 1954). Although in state service, this unit was under the operational control of the U.S. Army Antiaircraft Artillery Command (Moeller). According to USACE real estate case file, the Site remained a U.S. Army installation under the administrative jurisdiction of the Presidio of San Francisco.
On 1 March 1958, Battery D, 271st Antiaircraft Artillery Gun Battalion was reorganized as a missile battalion armed with the Nike-Ajax air defense missile system. With this reorganization, the unit moved to San Francisco Defense Area Site 59 at Fort Funston and was renamed Battery D, 271st Antiaircraft Artillery Missile Battalion (California Military Department 1958).
On 31 December 1958, the U.S. Army terminated the lease with Merck and Co. No documentation pertaining to improvements made to the Site by either the U.S. Navy or the U.S. Army has been found.

US Army Corps of Engineers Sacramento District History I (1990)
Location: AAA Battery 40 is located on Point San Bruno, which is south of Oyster Point Marina and north of the San Francisco Airport
Site History: A total of 8.62 acres was acquired for the AAA Battery 40 which was used by the United States (U.S.) Army as an anti aircraft missile launching site. On September 8, 1951, 8.13 acres was acquired by lease from Merck & Company and from June through November 1952, 0.49 acres was acquired by donated license. Two additional licenses (record of area not available) were dated June 29, 1952 (amended June 29, 1956) and November 10, 1952.
The property was declared excess to the General Services Administration on December 31, 1958. All 8.62 acres were disposed of: the lease for 8.13 acres was terminated on December 31, 1958, and the license for 0.49 acres was terminated on May 18, 1959. The other two licensed properties (no area listed) were terminated on October 7, 1958 and December 31, 1958.
The majority of the former AAA Battery 40 site is owned by Merck & Company. The property currently contains Merck & Company's warehouse, administrative building, a parking lot, and a vacant lot.
US Army Corps of Engineers Sacramento District History II (1990)
A total of 8.62 acres was acquired by the Sacramento District, US Army Corps of Engineers. Of this total, 8.13 acres was acquired by negotiated lease from Merck & Company on September 8, 1951 and 0.49 acres was acquired by donated license June through November, 1952. Two additional licenses (record of area not available) were dated June 29, 1952 (amended June 29, 1956) and November 10, 1952.
San Francisco Defense Area AAA Battery 40 was used by the U.S. Army as an air defense site.
The effective date that the property was reported as excess to the General Services Administration was December 31, 1958. On that date, the lease of 8.13 acres was terminated. On May 18, 1959, the license for 0.49 acres was terminated and the two other licensed properties (no area listed) were terminated on October 7, 1958 and December 31, 1958. For all properties except the 0.49 acres, the parties agreed to transfer of improvements in satisfaction of the government's obligation for restoration of the premises. The license of 0.49 acres was released without restriction, restoration, or recapture clause.
The M2 90mm Antiaircraft Gun
The M2 90mm Antiaircraft Gun in travel configuration
The M2 90 Antiaircraft Gun with wheeled bogies removed and outriggers extended
Prior to WWII, the primary US anti-aircraft gun was the 3-inch M1918 gun (76.2 mm L/50), a widely-used caliber for this class of weapon. Similar weapons were in British, Soviet and other arsenals. There had been several upgrades to the weapon over its history, including the experimental T8 and T9 versions developed in the early 1930s that were intended to enter service later in the decade.
However the Army became interested in a much more capable weapon instead, and on June 9, 1938 they issued a development contract calling for two new guns, one of 90 mm which they felt was the largest possible size that was still capable of being manually loaded at high elevations, and another, using assisted loading, of 120 mm caliber. The new design seemed so much better than developments of the older 3-inch that work on the 3-inch T9 was canceled in 1938 just as it became production-ready. By 1940 the second development of the 90 mm design, the T2, was standardized as the 90 mm M1, while its larger cousin became the 120 mm M1 gun.
A few hundred M1's were completed when several improvements were added to produce the 90 mm M1A1, which entered production in late 1940 and was accepted as the standard on May 22, 1941. The M1A1 included an improved mount and spring-rammer on the breach with the result that firing rates went up to 20 rounds per minute. Several thousand were available when the US entered the war, and the M1A1 was their standard AA gun for the rest of the war. Production rates continued to improve, topping out in the low thousands per month.
Like the German 88, and the British QF 3.7 inch AA gun, the M1A1 found itself facing tanks in combat, but unlike the others it could not be depressed to fire against them. On September 11, 1942 the Army issued specifications for a new mount to allow it to be used in this role, which resulted in the 90 mm M2, introducing yet another new mount that could be depressed to 10 degrees below horizontal and featured a new electrically-assisted rammer. It became the standard weapon from May 13, 1943.
In July 1941 it was decided that in future the 90-mm (3.54-in) gun and carriage would have to be capable of engaging sea and land targets as well. This meant a revision of the carriage as on the Ml carnage the gun could not be depressed below 0°, and the opportunity was taken to incorporate a radical redesign, The M2 carnage had a totally different design with a low firing platform carried on four outrigger legs when firing. It was much handier and quicker to get into action, and some versions also had a small shield. The main change, however, was to the gun, which became the M2 in which the ammunition feed for a new fuse setter and rammer was added, this making fuse setting much more rapid and accurate, and also raising the rate of fire to a possible 27 rounds per minute. Yet more accuracy and lethality was added in late 1944 when the 90-mm (3.54-in) gun was used as one of the first weapons on land to fire the new proximity-fused round, one of the most advanced weapon developments of the war years, Using this fuse one gunner managed to shoot down a Focke-Wulf Fw 190 fighter with a single shot as the unfortunate aircraft attempted to intervene in the Ardennes campaign. The 90-mm (3.54-in) gun and the proximity fuse were also instrumental in the defeat of the V-l flying bombs over southern England.
The 90-mm (3.54-in) gun in all its forms was manufactured in large numbers, By August 1945 a total of 7,831 of all types had been produced. This included some guns intended for static mounting only, and some guns were indeed used around the coasts of the continental USA in a dual anti-aircraft/ coastal role.
The 90-mm (3.54-in) gun was also used in a purely coast defence mounting in a special armoured turret, and at one stage it was proposed that these turrets would even have their own automatic loaders, thus removing the need for men to crew them in action as they would be aimed and fired by remote control. The 90-mm (3.54-in) gun was also used in M36 tank destroyers mounted on Sherman chassis, and there were several advanced designs involved in the production of a towed 90-mm (3.54-in) anti-tank gun, but none of these saw service.
Specification, 90-mm Gun M2 on Mount M2
Calibre: 90 mm (3.54 in)
Weight: complete 14651 kg (32,300 lb)
Dimensions: length travelling 9.021 m (29 ft 7.15 in); height 3.073 m (10 ft 1 in); wheelbase 4,166 m (13 ft 8 in); length of barrel 4.50 m (14 ft 9.2 in)
Elevation: +807-10°
Traverse: 360°
Maximum ceiling: 12040 m (39,500 ft)
Shell weight: 10.6 kg (23.4 lb)
Muzzle velocity: 823 m (2,700 ft) per second
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Updated 8 February 2016