From Dennis on Patreon:
"What rifles were between the M1 Garand and the M14? I went through Basic with an M14 and I know the M15 was supposed to be a BAR relacement. Google doesn't really find anything on the M2 - M13 rifles."

The Army had rifle for much more than just standard infantry use. They also adopted rifles for marksmanship practice, sub caliber firing of artillery, pilot survival (as the Army Air Force), and spotting. Here are the M2 through M13:

M2 - Springfield .22LR training rifle
M3 - Not used
M4 - Harrington & Richardson pilot survival rifle; bolt action .22 Hornet
M5 - Subcaliber .22LR adapter for 37mm guns
M6 - Ithaca pilot survival combination gun
M7 - Subcaliber .30-06 adapter for the 75mm recoilless rifle
M8 - Spotting rifle for the 106mm recoilless rifle
M9 - Subcaliber .30-06 adapter for the 106mm recoilless rifle
M10 - Not used
M11 - Not used
M12 - Harrington & Richardson .22LR training rifle
M13 - Remington .22LR training rifle