The Philippine Islands became United States territory in 1898, after the U.S. won over Spain in the Spanish-American War. Up to that point, Spain owned the Philippines for 300 years. But while the U.S. found the Philippines to be a good strategic position in the Pacific, the U.S. did not put adequate military protection on it. By not fortifying the islands effectively, they were prone to attack. This fact became a reality during World War II, when Japan decided to attack the Philippines and make it one of its possessions. But the U.S. government's lack of preparation did more than cause it to loose the Philippines. Insufficient fortification, a Europe First strategy, and underestimating the Japanese are only three of the factors which led to the deaths of thousands of American military personnel.
One of the factors leading to the downfall of the Philippines was its landscape, namely the fact that its mainland is surrounded by higher ground. While the military decided that the island of Corregidor would be used to keep foreign vessels out of Manila Bay, Corregidor was not adequately equipped for such a task. For example, Corregidor is only two miles from the Bataan Peninsula. However, it not only had very few weapons pointed toward Bataan, but those weapons were also inadequate to protect it. Bataan's landscape not only had mountains, such as Mount Mariveles (4,600 ft.), but it also had numerous valleys and ravines, which protected them from observation and shellfire. (1)
After Japan beat China in 1895 and Russia in 1905 with modern weapons, its only real challenger was the United States. Japan saw the Philippines as a potential bargaining chip. Therefore, Theodore Roosevelt decided to increase the islands' defenses. However, only one major combat unit was in the Philippine Division stationed on Luzon. (2) Meanwhile, Congress decided to station only minimal military defenses on the islands. The main island of Luzon received an insufficient number of combat troops and the U.S. Navy was kept stateside. In 1902 Corregidor was selected as the location for any possible prolonged sieges, if defending Manila became impossible. The Navy would be called from Pearl Harbor as reinforcement. High costs prevented an adequate number of troops from being stationed there and inefficient armament did not give those present the types of weapons needed to fight.
Most of [Corregidor's] heavy guns bore southward and westward and few bore on the Bataan Peninsula just two miles away. Moreover, most were rifles, with a relatively flat trajectory, and were incapable of lobbing a shell onto the reverse slope of a hill. Behind Bataan's many ridges an enemy could be expected to emplace siege howitzers which only the high-angle mortar batteries, Geary and Way, could touch. Also, all the batteries, the mortars included, were in open emplacements, vulnerable to plunging fire. To replace them with guns in turrets would be too costly; the House Appropriations Committee would never approve. To cover them with overhead concrete or armor protection would be almost as expensive and technically very difficult. In the end, all that the best efforts of many concerned officers could produce form 1909 onward was a series of remedial half measures. (3)
From 1915-1927, seaplanes were used for aerial observation. After World War I, counterbattery weapons from the Western front, such as 240 mm. Howitzers that could have protected Bataan were dispatched to the Philippines. However, they never arrived since Washington decided that diplomacy would protect the Philippines more than military weapons. A 1921 Nonfortification Clause in a treaty with Japan kept the U.S. from building up Corregidor or Guam's defenses for fifteen years. All the military could do was build a concrete tunnel system, completed in 1938, known as the Malinta Tunnel. Military cuts by the Harding Administration, meant the islands' manpower was "reduced to caretaker status." (4) Therefore, most of the Philippine Division consisted of Philippine Scout regiments since they did not cost as much as American units. Yet, while the U.S. was disarming in accordance with the treaty, Japan was building its military up.
Despite the lack of manpower, those stationed in the Philippines still faced the problem of the Navy stationed in Hawaii. Unless the Naval Fleet could travel across the Pacific and get past Japanese possessions, "the defenders eventually would be starved into submission." (5) Still, the military held on to the hope that if defenses on Corregidor could hold out for six months, the Navy would reach them. In 1924, this plan was codenamed War Plan Orange.
Its essential features were simple; the Army's "mobile" forces in Luzon would abandon Manila to retire into the natural jungle fortress of the Bataan peninsula, while the coast artillerymen protected their rear. The Navy would fight its way across the Pacific, seizing Japanese-held islands as it advanced. At some point, probably near Guam, a decisive Jutland-type naval battle would erupt between the battleships of the rival fleets and Japan would lose, giving America command of the seas and access to the beleaguered forces on Bataan and Corregidor. (6)
The problem with Plan Orange was that the Philippine Army did not have enough men to carry it out, "nor did the Navy have the logistical capacity to project its Pacific Fleet into the midst of Japan's advanced bases." (7) The equipment needed for the operation did not exist either.
The military realized the futility of the plan, therefore in 1934 Congress decided that instead of building up the defenses enabling the Philippines to be defended properly, the Philippines would receive its independence on July 4, 1946, through the passage of the Tydings-McDuffie Act. The U.S. military would leave the Philippines permanently and all defenses would be transferred to the new Philippine military. Lt. Gen. Douglas MacArthur, Chief of Staff of the Army, became the Field Marshall of the Philippine Commonwealth government. In 1935, he began working to build-up the Philippine military that would take over in 1946. Majors James B. Ord and Dwight D. Eisenhower assisted him.