The information on the first three stations is sketchy at best. It is known that the first three stations were destroyed before there completion. Babylon 1 and 2 were each destroyed by either human or Minbari factions not wanting the stations to go online. Babylon 3 was destroyed by accident. The sizes of the stations are unknown, but it is known that they were not as big as Babylon 4. All evidence points towards the destruction of the stations at early points in their construction.
Type: O'Neill Class Space Station
Length: 6km
Population: 500 000+
Location: 3hrs from Jump Point L-5 (Where Babylon 5 is stationed).
Defense Type: Extreme Defense Grid
Fighter Capacity: Unknown
Armament: Unknown (but all imprsessions point towards heavy duty weapons more powerful than that of babylon 5).
Parts from Babylon one, two and three were used for its construction therefore lessening its production cost. Babylon 4 made its first apearence in "Babylon Squared" in which it came back to unload the original crew ( 1300 of them ). It was seen again in the episodes "War Without End" part 1 and 2, at which time it was taken back by Jeffery Sinclair for a base of operations in the last Shadow War in which he gave it to the Minbari in his Minbari form of Valen. It did not survive all that long after the war.
Type: O'Neill Class Space Station
Location: L-5 Jump Point
Population: 250 000
Defense Type: Heavy Defense Grid ( upgraded from the Light Defense Grid when the 'ground pounders' came aboard in the episode "Gropos" ).
Fighter Capacity: 4 fighter squadrons.
Armament:
6 Plasma Cannons
6 Rapid Cycling Projection Cannons
6 Intercepters
More interceptors (these interceptors are the light defense guns which seem to have not been removed upon B5's defense grid upgrade)
Mine Launchers (though we have not seen these in acton they were mentioned in the episode "Gropos" where the B5 defense grid was upgraded)
Babylon 5 is the last of the Babylon stations. The stations were built for diplomacy and peace. Acting as trading centres ( with Babylon 4 also playing a serious military role ) the stations were considered important enough by many alien races to warrant their financial assistance. Even with the extra financial assistance Earth wanted to limit its funding for Babylon 5, and so therefore much of Babylon 5 has not been completed. In recent times B5 has become idependant and the base of operations for the forces of light.