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104 that there were too few steam tugs for the work.

Concentration

Concentration can be effected both by road and rail, the former being preferable for short distances, where the railway has only a single line. For example, an army corps that can be moved seventy-two miles by a double line in three days needs seven days to do the same distance by a single line, and only six days by road. But even where lines are double, it is frequently advisable to move a portion of an army by road to leave the railway free for the