Many people are aware of John M. Browning-designed weapons which were used on Bataan, such as the M1911 .45 caliber semi-automatic pistol, the M1917 Browning .30 caliber water-cooled machine gun (and M1919 air cooled variant), the M1918 Browning Automatic Rifle (BAR) and the M2 .50 caliber machine gun. But Browning designed an even larger caliber weapon that saw action on Bataan.
Coming out of the experience gained in the First World War, the United States sought to develop a large-caliber gun for use in aircraft. The Baldwin 37mm automatic gun was considered, but ultimately rejected. The famous John Browning was called upon in 1920 to look at this matter, and by 1924 he developed two 37mm prototypes for testing at Aberdeen Proving Ground. He developed two types given the U.S. Army had also developed a requirement for a lightweight 37mm gun for air defense against ground attack aircraft.
The anti-aircraft gun was eventually designated as the US 37mm Gun M1. It fired a 21-ounce explosive shell at a rate of fire of 120 rounds per minute. The effective altitude it could fire up to was 10,500 feet – the shell was fitted with a self-destruct mechanism set for this altitude. It could also be used against ground targets, with a maximum range of 8,850 yards (though the self-destruct mechanism would detonate after 4,000 yards of horizontal flight). Given the defense economies of the day, the gun was shelved. But in 1935, the Army took the anti-aircraft gun off the shelf and began an effort to design a suitable carriage for the weapon.
The first carriage made for the M1 was designated as the M3. It was a four-wheeled trailer with wheels carried on detachable axles. The gun itself was mounted on a levelling block that could be adjusted up to ten degrees to compensate for unlevel ground. The top of the carriage had the gun, gun sights, two seats for the layers (one for azimuth, the other for elevation) and a platform for the loader. Operation of the weapons in traverse and elevation was manual, as was sighting of the weapon, though later versions of the carriage (e.g. M3A2) had remote power-control motors and receiver dials for operating with a fire control predictor.
The Gun M1A2 on the Carriage M3 was standardized in 1938 and production began in 1939. Watervliet Arsenal made the guns the Rock Island Arsenal the carriages, and Bausch and Lomb the gun sights. Colt also made some of the guns until early 1941 when they shifted focus to aircraft cannon. Some 7,728 examples were produced until production ended in 1944.
According to an inventory of “Principal Weapons Philippines” dated 21 November, 1941, there was the following information on the “M1A2 37mm antiaircraft gun: ON HAND 66 U.S.; 0 P.A.; REQUIRED 96 U.S., 144 P.A.; SHORTAGE 30 U.S.; 66 P.A. [likely a typo, when 144 P.A. meant].”
As for identifying the units which operated these 66 M1A2 37mm anti-aircraft guns, it is hard to pin down. The 200th Coastal Artillery (Anti-Aircraft) Regiment of the New Mexico National Guard arrived in the Philippines shortly before the war began with 24 37mm guns, according to Morton. Cave mentioned that the 200th had 22 37mm guns arrayed for the defense of Clark Field just before the war began, though seven of them were defective and had been sent to Manila for repair. A Wikipedia page suggests the 60th Coastal Artillery (AA) Regiment on Corregidor and the forts in Manila Bay had 37mm guns, though other sources do not corroborate this.
In any event, in December, 1941, the 200th Coastal Artillery (AA) was split into two units (the 200th and the new 515th CA (AA) regiments when enough equipment was on hand to equip the two units, and they used their 37mm guns on Bataan to provide an important defensive capability, and were used to defend the airfields on Bataan (Bataan and Cabcaben), critical assets such as the I and II Corps artillery and/or command posts and important rear area installations, through the campaign.
When the final Japanese offensive broke through the Fil-Am defensive line in April, 1942, these two regiments were ordered to destroy their remaining weapons save those which could be used for infantry support, and form a line of defense as infantry on the high ground to the south of Cabcaben Airfield. As an example of what was left, by this time the 2nd Battalion’s Battery F had only one functioning 37mm gun remaining. On the night of April 8, they were the last line of defense between the approaching enemy and the vulnerable rear echelon area of Bataan. The anti-aircraft gunners’ mettle was not tested, however, as the surrender of Bataan occurred the next day, April 9, 1942.
By the end of the Bataan Campaign, the 200th had claimed 86 enemy aircraft shot down. The unit was equipped with the 3-inch anti-aircraft gun, 37mm anti-aircraft gun as well as .50 and .30 caliber machine guns. No doubt a portion of these claims were due to the M1A2 37mm anti-aircraft gun.
Cave, Dorothy, “Beyond Courage: One Regiment Against Japan, 1941-1945,” Sunstone Press, 2006
Hogg, Ian, “Anti-Aircraft Artillery,” The Crowood Press, 2002
Kirkpatrick, Charles, “ADA in Bataan: A Retrograde Operation,” Air Defense Artillery, Spring, 1985, at: http://www.airdefenseartillery.com/online/2010/ADA%20In%20Action/WWII/WWII/Retograde.pdf
Moore, George, “The Moore Report, Table of Organization & Equipment, Organization of the Coast Artillery in the Philippines,” at: http://corregidor.org/chs_moorerpt/moore1.htm
Morton, Louis, “The War in the Pacific: The Fall of the Philippines,” Center of Military History, Washington D.C., 1953
“Principal Weapons Philippines” listing, in 24 Jan 2012 discussion thread “Questions for John Gordon,” at: http://www.network54.com/Forum/594514/thread/1327371966/Questions+for+John+Gordon
“REMEMBERING CHARLES F. JAMES,” Congressional Record Volume 157, Number 44 (Wednesday, March 30, 2011), Senate, Pages S1973-S1974, From the Congressional Record Online, at: http://www.gpo.gov/fdsys/pkg/CREC-2011-03-30/html/CREC-2011-03-30-pt1-PgS1973-3.htm
Wikipedia page for 60th Coastal Artillery (AA) Regiment http://www.fact-index.com/6/60/60th_coast_artillery__aa__regiment.html