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Though the fall of Bataan ended all organized opposition on Luzon, it did not give the Japanese the most valuable prize of all, Manila Bay. So long as Corregidor and its sister forts across the entrance to the bay remained in American hands, the use of the finest natural harbor in the Orient was denied them. And before General Homma could report to his already impatient superiors in Tokyo that he had accomplished his mission, he would also have to occupy Mindanao to the south as well as the more important islands in the Visayan group in the central Philippines.
The campaign for the Philippine Islands was not yet over. Though he had won the most decisive battle of that campaign, Homma still had to take Corregidor and the islands south of Luzon before the Japanese could integrate the archipelago into the Greater East Asia Co-Prosperity Sphere.
Since the days of the Spaniards, Corregidor had been used as an outpost for the defense of Manila. (Map 23) By a system of semaphore signals from the island the Spaniards were able to receive warning of the approach of any hostile force in time to alert the forts in and around the capital. Later, they constructed minor fortifications on the island as an outer line of defense and as a screen for the larger guns emplaced along the Cavite shore south of Manila Bay, and at Fort Santiago in Manila. By 1898, when Admiral Dewey sailed into Manila Bay, the Spaniards had on Corregidor three large cannons, each with a range of about one mile. Two of these faced Cavite; the other pointed north toward Bataan. In addition the Spaniards had twelve other coastal guns to defend the approaches to the capital city: on El Fraile and Caballo Islands, which, like Corregidor, lay across the entrance to he bay; along the southern tip of Bataan; and along the Cavite shore.
After the cession of the Philippines to the United States, a vast construction program designed to defend Manila by sealing off the entrance to Manila Bay was begun. During the years before the first World War, forts were built on Corregidor and the adjoining islands in the bay. By 1914 the task was completed. The Americans could now boast of an elaborate defense system in Manila Bay, so strong as to justify the name Gibraltar of the East. Reflecting the doctrine of the era in which they were built, the forts were designed to withstand attack from the sea by the heaviest surface vessels then known.
The development of military aviation in the decade of the 1920s struck a sharp blow at the effectiveness of this carefully wrought and vastly expensive system of defenses. Nothing could be done to remedy the weakness of the forts, however, for by the Washington Naval Treaty of 1922 the construction of additional fortifications as well as the modernization of those already built was prohibited. Major construction after 1922, therefore, was limited to antiaircraft positions and to the tunnels dug into the solid rock of Malinta Hill on Corregidor, presumably as a storage area for supplies. When the Japanese attacked in December 1941, the defenses of Corregidor and the adjoining islands were little different from what they had been twenty-five years earlier.
Of the four fortified islands in Manila Bay, Corregidor, the site of Fort Mills, was the largest, measuring three and a half miles in length and one and a half miles at its widest point. With its bulbous head pointed toward the west and its tail stretching eastward, this tadpole-shaped island separated the bay entrance into a north and south channel. Corregidor had narrowly missed being two islands, for at the junction of the head and tail it narrowed to 600 yards and dropped to a height only slightly above sea level. This low area was known as Bottomside and contained two docks, the barrio of San Jose, shops, warehouses, a power plant, and cold-storage units. Directly to the east of Bottomside was Malinta Hill with its labyrinth of tunnels. Beyond, stretched the tail of the island, where a small airfield and a navy radio intercept station were located.
West of the narrow neck which connected the tail with the head of the tadpole was a small plateau known as Middleside. Here were located the hospital, quarters for commissioned and noncommissioned officers, a service club, and two schools for the children of the islands. Beyond, lay the heavy head of the tadpole, rising 500 feet above the sea. Called Topside, this area contained the headquarters, barracks, and officers quarters, grouped around the traditional parade grounds. The ground was high almost to the beach line where it dropped precipitously to the water's edge. Cutting into the cliffs were two ravines, James and Cheney, which gave access from the beaches to the crowded area above. These ravines, together with Ramsey Ravine which led to Middleside, were the critical points in the defense of Corregidor against hostile landings.
Critical also to the defense of Corregidor and the ability of its garrison to hold out against a sustained attack was the safety of its power plant. Fresh water for the island had to be brought by barge from Mariveles or pumped from the twenty-one deep wells on the island. Perishable food could be kept in that tropical climate only by power-driven cold-storage plants. The large seacoast gun batteries, though equipped with emergency power sets, relied on the power plant, and ventilation for the vast underground tunnels depended on electrically operated blowers. Although there were sixty-five miles of roads and trails on the island, much of the heavy equipment was moved over an electric railroad with thirteen and a half miles of track which led to all important military installations. The garrison, therefore, was dependent in a very real sense on the island's power plant, and it was natural that those concerned with planning the defense should make every provision to guard against its destruction by bombardment.
The most extensive construction on Corregidor was the tunnel system under Malinta Hill. Consisting of a main east-west passage 1,400 feet long and 30 feet side, the tunnel had 25 laterals, each about 400 feet long, branching out at regular intervals from each side of the main passage. The underground hospital was housed in a separate system of tunnels north of the main tunnel and had 12 laterals of its own. It could be reached either through the main tunnel or by a separate outside entrance on the north side of Malinta Hill. Opposite the hospital, under the south side of Malinta, was the Navy tunnel system, connected to the main tunnel by a partially completed low passageway through the quartermaster storage lateral. Reinforced with concrete walls, floors, and overhead arches, blowers to furnish fresh air, and a double-track electric car line along the east-west passage, the Malinta Tunnel furnished bombproof shelter for the hospital, headquarters, and shops, as well as a vast labyrinthine underground storehouse.
The armament of Corregidor was formidable. Its seacoast defense alone consisted of 23 batteries, many with their own names and traditions. Altogether, Corregidor had a total of 45 coastal guns and mortars, all of World War I vintage, ranging in caliber from 3 to 12 inches. (See Table) The longest range cannon were the two 12-inch guns of Batteries Smith and Hearn, with a horizontal range of 29,000 yards and all-around traverse. In addition, there were six 12-inch guns with a range of 17,000 yards, and ten mortars of the same caliber. Nineteen of Corregidor's guns were the 155-mm. GPFs, capable of a range of 17,000 yards. The ten 3-inchers had the shortest range. The supply of seacoast ammunition was ample but there was little of the type suitable for attacking land targets and no star shells to provide illumination for night fire. North and south of the island were extensive mine fields planted by the Army and Navy.
|Antiaircraft Artillery (Including Southern Bataan)|
|2||SL Sperry 60-inch*||10|
Source: Harbor Defenses Rpt of Opns, Annex C
Antiaircraft equipment consisted of 3-inch guns with a vertical range of 27,000 and 32,000 feet (depending on the type of ammunition used), .50-caliber machine guns, and 60-inch Sperry searchlights. Defending Corregidor from air attack were 24 of these 3-inch guns, 48 machine guns and 5 searchlights. Another battery of 3-inchers was emplaced on the southern tip of Bataan to tie in with these on Corregidor. Ammunition for the antiaircraft weapons was less plentiful than that for the seacoast guns, and there was a critical shortage of mechanically fuzed 3-inch high explosive shells.
Before the war, the Corregidor garrison consisted principally of headquarters, artillery, and service troops. The combined strength of the four fortified islands in manila Bay at that time did not exceed 6,000 men, most of whom were stationed on Corregidor. After 8 December the population of these garrisons swelled rapidly. First came the survivors of the Cavite naval base, then the headquarters and service troops from Manila. MacArthur's headquarters was established on Corregidor on 25 December and with it came the 809th Military Police Company, two ordnance companies, an engineer company, and service detachments. When Olongapo was evacuated on 26 December, the 4th Marines were also transferred to Corregidor, swelling its population by over 1,000 men. Before the first blow hit that island, it was already crowded with the men of all services and a dizzying pyramid of headquarters.
The defenses of the three other islands in the entrance to Manila Bay were hardly less formidable, proportionately, than those of Corregidor. Caballo (Fort Hughes), just south of Corregidor, was the next largest in size. Only about one quarter of a square mile in area, this island rose abruptly from the bay to a height of 380 feet on its western side. The east coast, which was lower than the rest of the island, was vulnerable to amphibious attack and a marine detachment of about 100 men was sent there to augment the garrison. later, 200 sailors from Corregidor were added to the marine detachment and Comdr. Francis J. Bridget, who had commanded the naval battalion in the Battle of the points, assumed command of the beach defenses. His force was almost doubled when the crews of four gunboats, about 225 men, were sent to the island. By the end of April the garrison of Fort Hughes numbered about 800 men of whom 93 were marines and 443 belonged to the Navy. The antiaircraft defenses of the island were tied in with those of Corregidor and consisted of four 3-inch guns. Seacoast artillery numbered thirteen pieces: two 14-inch guns, four 12-inch mortars, two 6-inch guns, three 155-mm. GPFs, and two 3-inchers.
ARMAMENT ON FORTS HUGHES, DRUM AND FRANK
|Fort Hughes (Caballo)|
|2||3-inch||(4 AA) 6|
|Fort Drum (El Fraile)|
|2||3-inch||(2 AA) 3|
|Fort Frank (Carabao)|
|1||75-mm. (beach defense)||3|
Source: Harbor Defenses Rpt of Opns,
Brig Gen Samuel L. Howard,
Rpt on 4th Marines, p. 18,
USMC Hist Sec.
About four miles south of Fort Hughes lay Fort Drum, the most unusual of the harbor defenses. Cutting away the entire top of El Fraile Island down to the water line and using the island as a foundation, the engineers had built a reinforced concrete battleship, 350 feet long and 144 feet wide, with exterior walls of concrete and steel 25 to 36 feet thick. The top deck of this concrete battleship was 40 feet above the low-water mark and had 20-foot-thick walls. Equipped with four 14-inch guns in armored turrets facing seaward, a secondary battery of four casemated 6-inch guns, and antiaircraft defense, the fort with its 200-man garrison was considered, even in 1941, impregnable to attack.
The southernmost of the fortified islands was Carabao, only 500 yards from the shores of Cavite Province. Except at one point along its eastern shore, the island rises precipitously from the sea in cliffs more than 100 feet high. On this uninviting island the Americans had placed Fort Frank, which late in 1941 had a military garrison of about 400 men, mostly Philippine Scouts. Its armament consisted of two 14-inch guns, eight 12-inch mortars, four 155-mm. GPFs, as well as antiaircraft and beach defense weapons.
All four forts in Manila Bay, as well as Fort Wint in Subic Bay, had been formed before the war into an organization called the Harbor Defenses of Manila and Subic Bays which, in August 1941, became a part of the Philippine Coast Artillery Command. Both were commanded by Maj. Gen. George F. Moore who also commanded the Corregidor garrison. The 5,700 men assigned to the Harbor Defenses were organized into three seacoast and one antiaircraft artillery regiments, headquarters, and service troops. The three seacoast units included the American 59th and the Philippine Scout 91st and 92d. The 60th, the antiaircraft regiment, was composed of Americans. About 500 Philippine Army soldiers in training were organized into the 1st and 2d Coast Artillery Regiments (PA), but operated under the control of the two Scout regiments.
General Moore commanded not only the seacoast and antiaircraft artillery but the beach defenses and inshore patrol as well. To exercise tactical control over all elements of his force, he had four major commands. Seaward defense he placed under Col. Paul D. Bunker who, in turn, commanded four groups, two of which covered North Channel and two South Channel. All antiaircraft units were under Col. Theodore M. Chase, commander of the 60th Coast Artillery. In addition to the normal mission of providing defense against air attack, Chase also maintained an air warning service for the fortified islands and for vessels in the bay. Though each fort commander was responsible for local defense, General Moore had an executive for beach defense who co-ordinated the plans for each of the islands. The inshore patrol remained a naval function, but under the principle of unity of command, Capt. Kenneth M. Hoeffel, USN, was under Moore's tactical control.
By the end of 1941 all that could be done in the limited time since funds had been made available in midyear to improve the defenses of Corregidor and the adjoining islands had been accomplished. But the basic weakness of the harbor defenses--their vulnerability to attack from the air and from their landward flanks--was never corrected. They accomplished their mission, the denial of Manila Bay to he enemy, without firing a single round at a hostile warship; Japanese cruisers and destroyers blockading the bay stayed well out of range of Moore's heavy guns. But when Bataan fell the flank protection of Corregidor disappeared and the fortress was left exposed to destruction by air and artillery attacks and to landings by hostile forces.
F O O T N O T E S
 The description of the fortifications in Manila Bay is based on the following sources: Harbor Defenses Rpt of Opns, pp. 1-16, Exhibits C, K, and M; American Fixed Coast Defenses in the Philippine Islands, Mil Rpts, No. 23, Nov 44, MID WD, p. 30; Lt Col Gwinn V. Porter, AA Defense of Corregidor, (paper prepared for Command and General Staff School, 1947-47), pp. 1-10; ltr, Admiral Rockwell to Gen Ward, 18 Jan 52, OCMH.
 Harbor Defenses Rpt of Opns, Exhibit K. The strength of the major units was as follows:
|HD Hq Brty||30||255||290|
|1st CA (PA)||50||428||12|
|2d CA (PA)||2||74||3|
 For a detailed account of the measures taken during the last six months of 1941, see Harbor Defenses Rpt of Opns, pp. 10-16, and Exhibit E.