I've done a little more research and it would appear that the U.S. Army may have incorporated jiujitsu into its combatives program sooner than I thought.
According to the information I've seen, a John J. O'Brien had lived in Japan and was among the first Americans to extensively study jiujitsu in Japan. A disciple of Tanaka and Inouye Sensei (Kishoku Inoue), he returned to the United States in 1900 from Nagasaki.
(One source states that he was a police officer in Nagasaki, but why the Japanese would employ an Occidental as a police officer in 1900 is a mystery to me.)
At any rate, he returned to the United States and is known to have provided lessons in jiujitsu to President Theodore Roosevelt in March and April of 1902. Roosevelt was a known boxing and wrestling enthusiast and according to all accounts fitted out a room in the White House specifically for jiujitsu practice.
Probably based on the contacts that he made while in Washington, in 1910 O'Brien was made a captain in the U.S. Army as part of the Army's modernization effort. He was assigned to developing the early H2H hand-to-hand combat program. This was the
beginning of the use of Ju-Jitsu as the Hand-to-Hand combat method of the U.S. Military.
Later, in the 1917-1918 period, Allen Corstorphin Smith was brought into the military combatives program by O'Brien and made a Captain because of his prior martial art experience as a Judo Blackbelt, which he received at the Kodokan in Japan.
Although O'Brien was the author of a book on JiuJitsu which was published in 1904, this book was intended for civilians. Smith was the author of the the first U.S. Army Hand-to-Hand combat "manual".