Specifications for Bath Iron Works hull 191, O’Bannon, were the same as sister Nicholas, laid down on the adjoining slipway:
GENERAL INFORMATION

Name: United States Ship O’Bannon.

Type: Destroyer.

Namesake: Marine Lt. Presley Neville O’Bannon. 

Navy Classification: DD 450.

Class: DD 445, Fletcher.

Authorized: 17 May 1938.

Builder: Bath Iron Works Corp., Bath, Maine.

Builder’s Hull Number: 191.

Keel laid: 3 March 1941.

Launched: 14 March 1942.

First commissioned: 26 June 1942.

Decommissioned: 21 May 1946.

Redesignated: DDE 450: 26 March 1949.

Recommissioned: 19 February 1951.

Decommissioned: 30 January 1970.

Disposition: Scrapped.

    Length Overall: 376' 5½"
    Extreme Beam: 39' 8"
    Normal Displacement: 2,050 long tons
    Draft: Light: 8' 1"; Mean: 13' 5" Deep: 22’8”
    Designed Complement: Officers, 34; Enlisted, 295
    Designed Shaft Horsepower: 60,000
    Designed Speed: 36 knots
    Screws: Two
    Rudder: One
    Stacks: Two
    Tactical diameter: 950 yards at 30 knots
    Endurance: 4,800 nautical miles at 15 knots.
O’Bannon, ordered 28 June 1940, was fitted with the original high, rounded bridge carried over from the Sims class. Like the other two 2,100-ton Fletcher-class ships completed in June 1942, Nicholas and Fletcher, she initially carried a 1.1-inch anti-aircraft cannon between the “53” and “54” 5-inch gunhouses.
    Primary: 5 x 5-inch/38 cal. in five single mounts
    Long-range anti-aircraft: 4 x 1.1-inch cannon in one quadruple mount
    Short-range anti-aircraft: 4 to 13 x 20mm Oerlikon in single mounts
    Torpedo Tubes: 10 x 21-inch in two quintuple mounts
    ASW: 2 racks for 600-lb. charges; 6 “K”-guns for 300-lb. charges
Her electronics were also typical:
    Radar: SC (air search) and SG (surface search), Mk 37 (fire control)
    Sonar: QC
The 1.1-inch gun tended to overheat and jam in service, however, and was replaced by a twin 40mm Bofors in the same location atop the aft deckhouse, which O’Bannon carried through the remainder of the war. In 1944, O’Bannon was further modified to carry two more of these twin mounts abreast the after stack and an additional two forward, below the bridge, in common with 157 of 166 then-active Fletchers:
    Primary: 5 x 5-inch/38 cal. in five single mounts
    Long-range anti-aircraft: 10 x 40mm Bofors in five twin mounts
    Short-range anti-aircraft: 7 x 20mm Oerlikon in single mounts
    Torpedo Tubes: 10 x 21-inch in two quintuple mounts
    ASW: 2 racks for 600-lb. charges; 6 “K”-guns for 300-lb. charges
From the beginning, O’Bannon also carried Mk 4 20mm single mounts, eventually mounting four in the waist and three on the fantail.

References: Friedman Bath Iron Works plans for hull no. 190 and crewmembers.