Looks like the old Model 1889, with a deeper crease.
Remember, Officers had a fairly generous 'wear-out' period for their uniforms, and on campaign, their most comfortable stuff was worn - while their Dress uniform may well have been up-to-date.
In his autobiography, when MacArthur returned from the Philippines prior to WWI - he mentions having to re-crease his Campaign Hat to better conform to the newly-issued, quite popular 'Montana Peak'.
Stylistically, he'd been away from the flagpole...
Vaya,
Scouts Out!