Navy Department began to develop Pearl Harbor Navy Yard 's dry dock and repair facilities with large appropriations , made available by Congress . But when the Pacific Fleet began using the harbor as an operating base in 1940 deficiencies were revealed inconsistent with its reputation as the ``Gibraltar of the Pacific . These were in process of being remedied when , on December 7 , 1941 , at about 7 :55 a .m , Japanese aircraft consisting of an estimated 150 to 200 fighting , bombing and...