Colt and FN
Yes
Have never heard of an underwater assault rifle. In the US, you must be 18 to buy a rifle, and 21 to buy a fully automatic rifle.
Ford, General Motors and Chrysler.
In Vietnam, for the first time in US history each and every US fighting man possessed a fully automatic rifle. During WWII, each and every US fighting man possessed a semi-automatic rifle (the M1 Garand).
Anyone that owns a legal AK47 will know how to gain information on their rifle, since they are worth about $14,000 each. People that do not know are generally asking how to create a fully automatic rifle, which is a serious crime in the US, with a penalty of 10 years in prison.
Yes they did! The standard US battle rifle was the M1, which was chambered in .30-06. In addition it was used by the Browning Automatic Rifle GPMG and some other weapons.
You will need to define assault rifle, and where you live. A TRUE assault rifle is a machine gun, and transfers of them are tightly regulated by the Federal government. What most people CALL an assault rifle is nothing but a semi-automatic rifle, and in most of the US, does not require a license to possess.
Could have been any number of US or European makers or an individual
As a private citizen in the US- you can't. The TAVOR was introduced AFTER the ban on registration of new fully automatic weapons in the US (May 1986).
An assault rifle is defined by the US State Dept and Dept of Defense as a "lightweight, select-fire rifle firing light to intermediate power rounds". The term "select-fire" means the rifle can fire EITHER semi-automatic or full automatic by the use of a selector (usually a switch). Since a TRUE assault rifle can fire full-auto, they are heavily regualted by the 1934 National Fireamrs Act. The Plinker Plus AR-15 is NOT an assault rifle, so the answer to your question is NO. If, however, you are looking for a basic entry level model semi-automatic rifle that bears a resemblence to the M16, you could do worse.
I like the stainless steel Ruger mini 14. You did not say what cal. or rifle or pistol.
Depends on what you mean by automatic guns, and the law where you live. You did not tell us where that is, so there is no way we can answer. Where I live you CAN legally own fully automatic firearms (machine guns) but they are horribly expensive. An M16 rifle that may be owned by a private citizen is between $12,000 and $16,000.