engine generating 500 hp. It had an internal supercharger and turned a 9 ft. two-blade Hamilton Standard propeller. The original configuration of the F4B-3 has a headrest fairing similar to the P-12E, but most were retrofitted with a headrest fairing capable of storing a liferaft. This later headrest fairing design was carried over to the F4B-4. F4B-4 (Boeing Model 235) The F4B-4 was nearly identical to the F4B-3, but incorporated a larger vertical fin to address the directional stability issues that plagued the F4B from its inception. The design was so similar to the F4B-3 that both aircraft had the same Boeing Model Number (235). The first nine aircraft (A-8912-8920) featured the same carburetor induction scheme as the F4B-3, but all following aircraft (A-8009-A-9053, 9226-9263 and 9719) featured a single oval carburetor intake on the port side only. F4B-5 A detailed specification was written for an F4B-5 as a minor development of the F4B-4 but was not proceeded with. Operational history U.S. Army Air Corps P-12s were flown by the 17th Pursuit Group (34th, 73rd, and 95th Pursuit Squadrons) at March Field, California, and the 20th Pursuit Group (55th, 77th and 79th Pursuit Squadrons) at Barksdale Field, Louisiana. Older P-12s were used by groups overseas: the 4th Composite Group (3rd Pursuit Squadron) in the Philippines, the 16th Pursuit Group (24th, 29th, 74th, and 79th Pursuit Squadrons) in the Canal Zone, and the 18th Pursuit Group (6th and 19th Pursuit Squadrons) in Hawaii. The P-12 remained in service with first-line pursuit groups until replaced by Boeing P-26s in 1934–1935. Survivors were relegated to training duties until 1941, when most were grounded and assigned to mechanic's schools. 23 P-12Cs, P-12Ds and P-12Es were transferred to the Navy for use as advanced trainers. Bureau numbers were 2489 through 2511. These aircraft were redesignated as F4B-4As U.S. Marine Corps F4Bs were flown by two Marine squadrons. VF-10M flew F4B-4s from February to July 1933. In June 1933, the squadron mission changed from Fighting to Bombing and was redesignated as VB-4M. By direction of MAJ Roy S. Gieger, Officer-in-Charge of Marine Corps Aviation, all VF-10M F4B-4s on strength be transferred to VF-9M at Quantico. By September 1933, VB-4M had been re-equipped with 16 F4B-3s. VF-9M based at Brown Field, Quantico flew F4B-4s, starting the transition in September 1932. In June of 1933, VF-9M received all of the F4B-4s transferred from VF-10M. VF-9M flew their F4B-4s