Bath Iron Works plans for hull no. 190. Source: National Archives

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

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 2100-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.