boats would shift to battery when the order to Dive went down. Give the snipes(2 in each room) as much time as possible to get the engines shut down, shut the main induction valve in each room, BOTH exhaust valves on EACH ENGINE, shift the fuel and oil pumps to slow speed, shut the cooling water valves on the sea chests, secure any aux. machinery in the room, etc., in less than 30 sec. As the Electric Motors actually drove the shafts, all they needed was a source of Juice. Battery was instantaneous, with speed changes as simple as turning the rheostats for the motors after shifting the bus from GEN to BATT.
Usual procedure was prepare to dive (shut down the engine(s), shift to battery bus), Dive(turn the rheostats to full lock in emergency or whatever speed the OOD called up and get the hell down). once down and trimmed, slow down to 1/3 bell, and power down all un-necessary loads.