Complex sentence: The US Army, while never formally adopting the M1895, purchased 2 in 1902 for testing and then 140 in 1904 and they would see intermittent use by Army and National Guard Units at least until 1921.
Split into simpler sentences: The US Army, while never formally adopting the M1895, purchased 2 guns in 1902, followed by an additional purchase of 140 guns in 1904. These would see intermittent use by Army and National Guard Units at least until 1921.