The Harbor Defenses of Manila and Subic Bays ("Coast Defenses of Manila and Subic Bays" until 1925) (a.k.a. CD/HD Manila Bay) were a United States Army Coast Artillery Corps harbor defense command, part of the Philippine Department of the United States Army from circa 1910 through early World War II. The command primarily consisted of four forts on islands at the entrance to Manila Bay and one fort on an island in Subic Bay.McGovern and Berhow 2003, pp. 7-12
Background and construction The United States acquired the Philippines as a territory as a result of the Spanish–American War in 1898. The Taft Board of 1905 recommended extensive, then-modern fortifications at the entrance to Manila Bay. The islands there had been declared military reservations on 11 April 1902. Accordingly, El Fraile, Carabao, Corregidor, Grande, and Caballo Islands in the Philippines were to be fortified and incorporated into the harbor defenses of Manila and Subic Bays, protecting the bases of the US Asiatic Fleet and the Philippines' capital and chief port of Manila. From circa 1905 to 1915 the following forts were built: Fort Mills (Corregidor), Fort Hughes (Caballo Island), Fort Drum (El Fraile Island), and Fort Frank (Carabao Island) at the entrance to Manila Bay, as well as Fort Wint (Grande Island) at the entrance to Subic Bay. The forts were designed for one purpose: to prevent enemy surface vessels from entering Manila Bay or Subic Bay. They were designed before airplanes became important in war, and (except for Fort Drum) were vulnerable to air and high-angle artillery attack, being protected only by camouflage. Except for the mortar batteries, the turrets of Fort Drum, and the two guns of the 1920s Batteries Smith and Hearn, the forts' guns had restricted arcs of fire of about 170°, and could only bear on targets entering the bay from the west.
In an exercise in 1907 at Subic Bay, a US Marine battalion of the Advanced Base Force commanded by Major Eli K. Cole emplaced forty-four heavy guns for coast defense in a ten-week period, due to the Eight-eight fleet war scare with Japan.Allan R. Millett, Semper Fidelis: The History of the United States Marine Corps, (New York City, NY: The Free Press, 1991). These were operated by the Marines until circa 1910, when Fort Wint on Grande Island was completed.
Corregidor was by far the largest fortified island in the Philippines, strategically located at the mouth of Manila Bay. Fort Mills was built there and was substantially complete by 1911. At that time the island had six guns on disappearing carriages, twelve mortars, two disappearing guns, five disappearing guns, and four guns on pedestal mounts. Three additional batteries of two guns each followed within a few years; Battery Keyes in 1913 and Batteries Cushing and Hanna in 1919. As the only fort on a sizable island, Corregidor had most of the barracks along with administrative and headquarters buildings.Berhow 2015, pp. 222, 233-240 The island also had 13 miles of electric railway, an unusual feature in US forts.Morton, p. 473
Fort Drum on El Fraile Island, completed in 1914, was the second-most powerful fort in Manila Bay and the most unusual. The island was partway between Corregidor and the Cavite province shore south of that island. El Fraile was razed to the waterline and a "concrete battleship" structure built on it. Fort Drum was both the only sea fort and the only fort with turrets in the post-1885 US fort systems. Two turrets housing two guns each were atop the fort. The 14-inch guns were the only M1909 14-inch guns deployed; they were specially designed for Fort Drum's turrets. Each side of the fort housed a pair of guns in casemates. The turrets proved impregnable to both air attack and plunging fire from Japanese howitzers, remaining in action until the surrender on 6 May 1942.Morton, pp. 486-487, 540
Forts Hughes and Frank, both completed by 1914 (except Fort Hughes' mortars in 1919), were generally similar in that each had two one-gun batteries of guns. Fort Hughes was just south of Corregidor, while Fort Frank was at the southern entrance to Manila Bay, close to the Cavite province shore. In addition to the 14-inch guns, Fort Hughes also had four mortars, two disappearing guns, and two guns. Fort Frank also had eight 12-inch mortars and two 3-inch guns.
Fort Wint was completed in 1910, on Grande Island at the mouth of Subic Bay, at some distance from the other fort. It had the least armament; two disappearing guns, two disappearing guns, and four guns.
During the American participation in World War I CD Manila Bay had an authorized strength of 21 companies. In 1919 the defenses' commander was Colonel Calvin Hearn.Order of Names at Corregidor.org The 59th Coast Artillery Regiment was transferred to the Philippines in 1921, including some GPF guns.Gaines, pp. 34-35 From 1922 parts of the defenses were garrisoned by units of the Philippine Scouts, which were US Regular Army units primarily composed of Filipino enlisted men and US officers. In 1922-23 fifteen companies of Philippine Scouts were authorized, initially numbered the 257th through 289th companies of Coast Artillery.Berhow 2015, p. 432 In 1924, as part of a forcewide conversion of the Coast Artillery Corps to a regimental system, the 59th CA was reorganized as a tractor drawn regiment and the 91st and 92nd Coast Artillery Regiments (Philippine Scouts) were created from the existing companies. In 1935 the 59th CA was further reorganized as a harbor defense regiment.Gaines, pp. 34-35, 48
The last new armament in HD Manila Bay until 1940 was significant but small in quantity: Batteries Smith and Hearn at Fort Mills, completed in 1921. These had one M1895 gun each on an M1917 long-range carriage, with an elevation of 35° and 360° of traverse, with range increased from on a disappearing carriage to .Battery Hall, Fort Saulsbury, Delaware at FortWiki.com, with the same weapons as Batteries Smith and HearnBerhow 2015, p. 61 The disadvantage was that the guns were completely unprotected. This type of battery was also built at eight other harbor defense commands in CONUS, Hawaii, and Panama.Berhow 2015, pp. 227-228 In 1923 the Washington Naval Treaty prohibited additional fortifications in the Pacific, thus the Philippine forts received no further weapons until after 1936, when Japan withdrew from the treaty, rendering it void. Ironically, had these batteries been modernized, they would have been casemated, restricting them to a 180° field of fire, and would have been less useful against the Japanese on Bataan. One result of the Washington Naval Treaty was the diversion of twelve 240 mm howitzers on a ship bound for the Philippines to Hawaii, where they were placed on fixed mountings on Oahu. The total lack of mobile high-angle artillery was a major impediment to the defense of the Philippines.Berhow 2015, p. 194
Spare gun barrels were provided near some batteries on Corregidor, including Smith and Hearn, due to the inability to re-line used barrels except at specialized facilities in the continental United States (CONUS).
Minefields Manila Bay and Subic Bay had Army-operated minefields available from circa 1915 (not usually deployed in peacetime) as well as naval mines laid in 1941. These minefields were designed to stop all vessels except submarines and shallow-draft surface craft. In Manila Bay, two controlled minefields were placed by USAMP Colonel George F. E. Harrison, one extending west from Corregidor to La Monja Island, and the other extending north from Corregidor to the Bataan Peninsula east of Mariveles Bay. Both of these were operated from Corregidor. Also, in mid-1941 US Navy minefields of contact mines were laid between Mariveles Bay and La Monja Island, and between Corregidor and Carabao Islands, to close off the bay approaches not covered by Army mines. The Subic Bay minefield was laid in July 1941 and operated from Fort Wint, with the controlled Army mines in the ship channel, and naval mines to the sides of the channel.Lewis, pp. 83-89Forts in the Philippines at American Forts Network
On the night of 16–17 December 1941 the passenger ship SS Corregidor (formerly HMS Engadine) hit a mine and sank near Corregidor Island. The ship departed Manila that night without obtaining permission from the US Navy's Inshore Patrol, which meant the minefield operators were not alerted that a friendly ship was departing the harbor. The minefield's usual state in wartime was active, which meant they would detonate on contact. This probably applied to the mines in the designated ship channel as well. When the ship was spotted, some accounts state that Colonel Paul Bunker, commander of the Seaward Defenses, ordered that the minefield remain active. Due to wartime conditions, no official investigation was ever conducted, leaving many questions open. The location at which the ship sank has not been determined, for example.Some accounts indicate the ship sank near La Monja Island, but this would mean the ship somehow got through the Corregidor-Bataan Army minefield. Accounts state that US Army officers informally told Filipino reporters that the mines were placed in safe mode immediately after the sinking. The ship was crowded with 1,200 to 1,500 persons, mostly Filipino civilians evacuating to Mindanao. 150 Philippine Army personnel and seven Americans were on board, along with several 2.95-inch mountain guns badly needed by the forces in the southern Philippines. Three PT boats (PT-32, PT-34 and PT-35) picked up 282 survivors, of which seven later died.Discussion with quotes from several sources about the sinking of SS Corregidor at Corregidor.comDiary of CPT George Steiger, entry for 19 December 1941
The Malinta Tunnel
The main part of the Malinta Tunnel complex was built on Corregidor from 1932 to 1934, with construction continuing until the Philippines was invaded by Japan in December 1941. Most US forts of this era had only small underground facilities, and this tunnel complex was the largest in the US coastal defense system. Due to the Washington Naval Treaty's prohibition on new fortifications, most of the complex was built without appropriated funds, using Filipino convict labor for unskilled tasks, and explosives slated for disposal. During the siege, the Malinta Tunnel proved important to the survival of the Philippine government, the military high command, the medical staff, and numerous civilians.Strong, Paschal N., The Lean Years, p. 2 at Corregidor.org
World War II
On 26 July 1941 Lieutenant GeneralMajor General when recalled, promoted two days later. Douglas MacArthur was recalled to active duty and made the commander of U.S. Army Forces in the Far East (USAFFE), which included the Philippine Scouts and the Philippine Commonwealth Army. MacArthur had been an official US advisor to the Philippine forces as a Philippine Field Marshal from 1935 to 1937, and had continued this function as a civilian since his retirement from the U.S. Army at the end of that period.Morton, p. 19 In July 1941 the harbor defenses were commanded by Major General George F. Moore, whose Philippine Coast Artillery Command was headquartered at Fort Mills, on Corregidor. At this time there were 4,967 troops assigned to the Harbor Defenses.
The major units under the harbor defense command in World War II included: 59th Coast Artillery (Harbor Defense) (U.S. Regular Army) 91st Coast Artillery (HD) (Philippine Scouts) 92nd Coast Artillery (Tractor Drawn) (Philippine Scouts) 60th Coast Artillery AA (U.S. Regular Army) 1st Coast Artillery (Philippine Army)Morton, p. 478 2nd Coast Artillery (Philippine Army)
Other antiaircraft units in the Philippines included: 200th Coast Artillery AA (New Mexico National Guard) (arrived September 1941) 515th Coast Artillery AA (New Mexico National Guard, Philippine Army) (organized December 1941 from the 200th CA AA and Philippine Army)
Antiaircraft units