thumb|right|260px| M1910 gun fires at Fort MacArthur, San Pedro, California.
thumb|260px|right| mortars, similar to those of Battery Koehler.
Fort Frank (Carabao Island, the Philippines) was one of the defense forts at the entrance to Manila Bay established by the United States. The entire island was designated as Fort Frank, in honor of Brigadier General Royal T. Frank, as part of the Harbor Defenses of Manila and Subic Bays built by the Philippine Department of the US Army in the early 1900s.
Geography
Carabao Island is located near the southern end of the entrance to Manila Bay about off the coast of Maragondon in the province of Cavite. The long, narrow island is surrounded by sheer cliffs over . The whole island and fort has an area of with the highest elevation at .
Battery Greer was named for Col. John E. Greer, an Ordnance Corps officer. Battery Crofton was named for Captain William Crofton, an infantry officer. Battery Koehler was named for 1st Lt. Edgar F. Koehler, killed in the Philippine–American War. Battery Hoyle was named for Brigadier General Eli D. Hoyle, a Spanish–American War veteran who was an administrator in World War I. On 20 March 1942, thirty-four soldiers were killed by Japanese artillery when a round ricocheted into a tunnel at Battery Crofton.