Sawtooth500Why did the first early diesels (F and E units) not have external catwalks, whereas their successors all have external catwalks? And why do some locomotives still today (primarily passenger) lack catwalks, given their utility?
Separate cases for the E and F units. Passenger locomotives like the E units were styled to be sleek and aerodynamic looking as a selling point. In the case of the "F" units they were designed to be used as a 4-unit set with a cab unit facing out at each end, so rearward visibility wasn't important. If you peel of the sheet metal on an E or F unit you will see a truss, just like a bridge down each side of the locomotive. this truss provides all the strength. On a GP or SD series locomotive the strength is provided by a welded girder underframe. On all locomotives you can walk from one end to the other without getting off the locomotive. On E and F units the walkway is inside with low headroom.
Cowl units are primarily that way for aesthetics and protection of a person moving to/from the cab while underway, but apparently, the F40s are partly for structural strength, as well.
-Don (Random stuff, mostly about trains - what else? http://blerfblog.blogspot.com/)
I suppose because the E's and F's were intended for passenger trains, or freight trains that weren't involved in any switching operations. Also the prime mover could be accessed from the interior of the loco, and didn't require walking outside.
Another matter at the time, was that streamlining was a big deal, and they wanted the new diesels to look similar to the airliners of the day. Probably passenger appeal had alot to do with it.
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