While the V2 made use of a key element of inertial navigation systems (the Pendulous Integrating Gyroscopic Accelerometer [1]), it was apparently only used to cut off the motor when the desired velocity was reached (the other elements of the control system guided it on a trajectory which curved from vertical to 74 degrees as a function of time, with the azimuth determined by the positioning of the rocket on its launch stand prior to firing.) Consequently, the performance of modern inertial navigation cannot be deduced from V2 accuracy (or, rather, the lack thereof.)

[1] https://en.wikipedia.org/wiki/PIGA_accelerometer