Advanced Research Projects Agency Network

(ARPANET).

A

 wide area 

network

 developed 

in

 the 1960s by the 

Advanced Research Projects Agency

 of the U.

S

.Department of Defense, that linked government sites, academic research sites, 

and

 industrial sites around the world.Later, the military communications part split off 

and

 was 

named

 MILNET.

ARPANET

 was the testing ground 

and

 original 

backbone

 of the 

Internet

.