From Our Jungle Road to Tokyo, by Robert L. Eichelberger (Gorget Books, 2017; first published 1950), Kindle Loc. 3745-58:
In the main, these island assaults [“52 D-Days” between Dec. 1944 and Aug. 1945] were made with small units of such divisions as the 24th, the 40th, the Americal. One of the colorful outfits which took part in the enterprise was the 1st Philippine Infantry. This was an American regiment made up of American Filipinos (most of them from California) who had volunteered to fight for the homeland. The regiment was organized as the result of a suggestion by the then President Quezon to President Roosevelt. I used the 1st Philippine Infantry also in the subjugation of Samar, and its record was excellent.
As a matter of fact, by this time I had requested that General Irving be assigned to me as the boss of what we called Eighth Army Area Command. This meant that Fred Irving would command combat activities in Samar as well as supervise military areas behind us. Fred fell heir not only to the 1st Philippine Infantry but to an entirely separate outfit of American Filipinos known as the 1st Philippine Battalion. These troops had sound training. When GHQ requested Spanish-speaking American troops to serve as military police in Manila, Irving recruited them from the 1st Philippine Battalion.
Ten amphibious landings were necessary to wipe out the Japanese positions astride the over-water route south of Luzon. Usually we sent Americans ashore for the quick capture of an island and then moved in native irregulars and guerrillas to serve as garrison troops. In this way we were able to use our combat veterans over and over again. Much of the credit for the speed and efficiency of the enterprise belongs to the motor torpedo squadrons of Seventh Fleet. By day and night raids, by constant surveillance, they disrupted interisland traffic and blocked evacuation of enemy units to Luzon.