Where is the starter?
Interesting question. On more modest sized, multiple thousands of HP, locomotive and marine diesels they use compressed air to start the engines. Blow air into a cylinder and use it as an air motor to get the crank turning.
Ones I saw in a power plant used compressed air from a 500 gallon sized tank. It had its own smaller diesel engine to run a compressor to charge the tank. Kind of surprised me, I thought they would have used the generators, as electric motors, to spin the engines to get them started. These generators were at a REA site and were only used as supplemental generators on the already up grid. So, there was electricity present for the "motors."