This smartly-turned out sailor is ‘presenting arms’ with the M1903 ‘Springfield Rifle’.  First introduced in 1903, this rifle was widely used by all U.S. Forces and saw extensive service in WW1 and beyond. 
Our sailor wears the standard web cartridge belt with 10 ammunition pouches attached as well as his water canteen and bayonet scabbard. 
Befitting a Naval Landing Party he also has his navy bellbottom pants neatly tucked into long canvas gaiters.