Keith Laumer was a well-known and respected science fiction writer
who, during the 1960s, began writing short stories featuring sentient
robotic tanks known as Bolos, huge and powerful combat machines
that 
often seemed to understand such concepts as "honor" and "duty"
better 
than some of their human commanders.
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Laumer died a few years ago, and his work will be missed . . . 
especially
his stories and novels about Retief, the always-ready, 
always-brilliant
galactic diplomat. The Bolo stories have enjoyed a kind
 of renaissance,
however, as Baen Books began publishing a series of 
collections of new
Bolo stories, written by various authors. My "Hold 
Until Relieved"
appears in the fourth of these: 
Bolos Book 4: Last Stand.
http://web.archive.org/web/20070609114151/http://users.stargate.net/~whkeith/htm/bolo.htm