Proposed armament was 6 x 0.50 caliber heavy machine guns or 6 x 20mm cannons - in either case the armament was to be mounted in the wing leading edges just outside of the spinning propeller blades diameter. However, this armament was never fitted to any of the test articles mentioned. To undertake its various intended roles, the XF8B was fitted with an internal bomb bay as well as underwing hardpoints which allowed for a maximum ordnance haul of 6,400lbs. In place of bombs, the aircraft was slated to carry 2 x 2,000lb torpedoes or an equal amount in weight of fuel - an internal load as well as external jettisonable tanks for excellent range.
Dimensions included a length of 43 feet, 3 inches, a wingspan of 54 feet and a height of16 feet, 3 inches. As completed, the aircraft became the largest (and therefore heaviest) single-seat, single-engine prop-powered fighter ever flown up to that time. The dimensions made for an aircraft with an empty weight of 6,135lbs and a Maximum Take-Off Weight (MTOW) of 9,840lbs. This made for one particularly large and heavy carrier-based fighter design. To help offset its size aboard the space-strapped American carriers, the wing elements were engineered to fold inwards, hinged just outboard of the main landing gear legs. This reduced the wingspan considerably and was common practice for navy aircraft - a feature still present today.
The initial flight of the prototype proved the design a general success though some minor elements had to be revised. The second prototype airframe was completed in January of 1945 but this had to wait for an available powerplant to be delivered and installed and thusly did not fly until after the war. Service trials then began for Prototype One which ran from mid-March 1945 to mid-April and the USN liked what Boeing had to offer on the whole despite it was a more expensive and heavier aircraft than first envisioned.
It was about this time that the USN was close to agreeing on a production course with Boeing though Boeing's commitment still lay with U.S. Army (and later U.S. Air Force) bombers and the USN had begun serious experimentation with jet-powered aircraft on carrier decks before the war's end. The conclusion of the war in Europe came in May of 1945 and the Pacific War ended that September, bringing about an end for the "do-everything" carrier-based fighter. The piston-powered fighter, as a whole, had more or less reached its apex in performance by the end of the war, capping its reign in the 3,000-4,000 horsepower range. Development of jet engines would soon enough offer the needed performance gains for USN fighter and bomber service to negate the need for a new expensive propeller-based airplane. As such, USN interest in the XF8B fell to the wayside as it looked to its future post-World War 2 needs in jets. The XF8B marked its last serious piston-powered fighter design under review.
Boeing also realized the end of the line for its XF8B proposal and began to reduce work on the product. The original order for three flyable aircraft was eventually completed and these continued in testing with the USAAF and USN into 1946 and 1947 respectively. Boeing's part in the XF8B ended soon after with all prototypes eventually scrapped.