The P-84B was the first production version of Republic's Thunderjet fighter. An initial contract approved in January 1946 called for 15 pre-production YP-84A service test prototypes and 85 production P-84B models.

The P-84B was virtually identical to the YP-84A with a 4000lb.-thrust Allison J35-A-15C engine. Armament consisted of six M-3 0.50 caliber machine guns, four in the fuselage and two in the wing roots.

Delivery of the P-84B began in the summer of 1947 to the 14th Fighter Group at Dow Field in Bangor, Maine. Subsequent orders in June of 1947 called for 141 additional P-84B airplanes. In the new aircraft, retractable launchers for eight 5-inch rockets underneath the wings supplemented the machine gun armament. The last P-84B was delivered in February of 1948.

The P-84B had a maximum speed of 587 mph at 4,000 feet altitude. Its initial climb rate was 5,200 feet per minute. The airplane's service ceiling was 40,750 feet and it had a range of 1,282 miles.

The sixth production P-84B, serial number 45-59502, was assigned to the 14th Fighter Group. It was later assigned to Muroc Air Force Base for Service Test duties.