In some two-stage systems, damper doors would be opened or closed by the pilot in order to bypass one stage as needed. Some systems had a cockpit control for opening or closing a damper to the intercooler/aftercooler, providing another way to control temperature. Rolls-Royce Merlin engines had fully automated boost control with all the pilot having to do was advance the throttle with the control system limiting boost as necessary until maximum altitude was reached.