After Navy officials had been forced to explain to Congress why four production contracts had been signed before avionics testing had been completed, action was taken; Grumman and the US Navy scrambled to improve the design. The unreliable rotary drum computer was replaced by a Litton L-304 digital computer and various avionics systems were replaced – the upgraded aircraft were designated E-2Bs. In total, 49 of the 59 E-2As were upgraded to E-2B standard. These aircraft replaced the E-1B Tracers in the various US Navy AEW squadrons.