In the doghouse

[phil55]

  I was wondering what the purpose of the doghouse is on a steam locomotive tender. Did a crew member ride in it or was it for some other purpose?

[babbo_enzo]

Well, sure not for a DOG

Normally, freight operations required both a head-end brakeman and a brakeman at the rear of the train.  Often, there wasn't a lot of extra room in the cab.  The fireman didn't always like to share his seat with the brakeman and there wasn't really enough room to stand without getting in the way of the fireman.  By 1937, new locomotives were built with enough room to seat the head-end brakeman in the cab.  Older locomotives were modified during shopping with a small cabin on the top of the tender for the head-end brakeman.  This was called a "doghouse".

For example see also this discussions:
http://www.trainorders.com/discussion/read.php?10,1217379

http://www.railroad.net/forums/viewtopic.php?f=13&t=25929

http://forums.mylargescale.com/12-railroad-operations/18037-what-did-head-end-brakeman-doghouse-do.html

and this book:
https://books.google.com/books?id=AzJCeF3oUnUC&pg=PA182&lpg=PA182&dq=doghouse+on+a+steam+locomotive+tender&source=bl&ots=gNME4kaUt7&sig=bYPVkvlo0JD5eFurvA751l4bexs&hl=it&sa=X&ei=w1nKVOj_Lob2yQTFxYDgBg&ved=0CFwQ6AEwCQ#v=onepage&q=doghouse%20on%20a%20steam%20locomotive%20tender&f=false

[Lenny53]

IIRC they were often found on locos used in helper/pusher service that performed a lot of backward moves.