[en] A data acquisition system consisting of time–of–flight scintillation counters, associated electronics, and a PDP–9 computer was developed and installed for use with the SLAC 40 in. hydrogen bubble chamber (HBC). The system was designed for optimum timing resolution subject to the limitations imposed by the HBC design and was used primarily to determine the momentum of a neutral beam of KL0 and neutrons, by measuring time–of–flight from a production target to the chamber. The system was also used to trigger the HBC flash only when a low momentum beam particle was recorded. Furthermore, this paper gives the details of the design and operation of the hardware and of the procedures necessary to incorporate the time–of–flight information into the more conventional bubble chamber picture analysis.