CORREGIDOR. Tip of Bataan, upper left.

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.

The Harbor Defenses of Manila Bay

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 the 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.¹

The development of military aviation in the decade of the 1920's 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.