The first part of this little book, namely “The Battle of the Iron
Horse,” appeared, very much as it stands, in the September number of
_The National Review_, 1925, and I have to thank the editor, Mr. Leo
Maxse, for his kindness in allowing me to republish it.
The second part is based partially on personal experience and
reflection, and partially on the lectures and papers of others. In the
war, the tank brought me to realize the enormous possibilities of
cross-country movement, and, in 1921, I set down my ideas as regards its
commercial future in a pamphlet entitled _Economic Movement_, which was
published in 1922.