Sentence:  Colonel Elbridge Colby in "Army Talk" tells us that the shelter-half, or “<WSD>pup tent</WSD>” made its debut during the Civil War. It seems to have been first christened “<WSD>pup tent</WSD>” by the Sixth Iowa Infantry at Memphis in 1862 and appears to stem etymologically from the same soldierly self-ridicule that resulted in such terms as “dogface” and “dog tags.” 
Meaning of the word marked with <WSD> tags:  A shelter half, one of two halves comprising a shelter tent or dog tent.