CAR-15 is a common name applied to many carbine variants of the Colt AR-15 rifle (adopted by the USA as the M16 rifle) in both military and civilian service.
A common point of confusion is whether the Colt carbines are assault rifles or submachineguns.
The original assault rifle, the Sturmgewehr_44, introduced three key features:
select fire, with both semi-automatic and fully-automatic modes;
an intermediate cartridge, between a pistol and rifle round in power;
a large-capacity detachable box magazine, usually 20 rounds or higher.
Criterion two is exclusive of submachineguns. They, by definition, fire pistol cartridges. The Colt carbines meet all three criteria of the STG-44 and are assault rifles, however much they may externally resemble submachinguns in size.