In this study, an ultrasonic digital beamformer based on subarray processing of 1-bit delta-sigma (Delta Sigma) oversampled echo signals is presented. The single-bit oversampling Delta Sigma conversion simplifies the coherent processing in beamforming with improved timing accuracy. Subarray processing also aims to simplify the beamforming complexity, where the partial-beam sums (low-resolution beams) are acquired from small subarrays, and then these partial beams are coherently processed for producing high-resolution beams. In the Delta Sigma subarray beamforming, the Delta Sigma coded echo signals are summed over the subarray channels, and then these partial beam-sums are first Delta Sigma demodulated, then processed for beam-interpolation, followed by coherent summation. This method requires decimation filtering of partial-beam sums from each subarray. The hardware complexity of the Delta Sigma subarray beamformer is compared with other beamformers and significant front-end savings are explained. The system is tested experimentally and the results are compared with others using B-scan images reconstructed from archival experimental raw RF data. Both wire targets and cyst phantom are used to show the differences in Signal to Noise Ratio (SNR) and Contrast to Noise Ratio (CNR) measurements.