EARTH FLEET SIZE

First, please note that Earth Alliance, according to the novelization of "In the Beginning", had a fleet of some 50,000 starships. This however is not what I based my own figures on. I based my fleet size figures on the hull registration numbers seen on the sides of the Hyperion type vessels, which are our only indication of fleet sizes in the Babylon 5 universe.  The EAS Hyperion seen in "A Voice in the Wilderness" had a hull registration number of "21,494 IAK."  We don't know what the letters stand for, but the numbers speak for themselves.  On the side of the Hyperion, the large number read 21, obviously to denote that the Hyperion was in the 21,000 line of capital ships made by the Earth Alliance.

The highest number seen on a Heavy Cruiser was at the "Battle of the Line" in the original TNT movie "In the Beginning."  The full registration number was not seen, but the family number was, 48, suggesting that this vessel was about the 48,000 starship built by the Earth Alliance, which falls well within the figure stated in the novel "In the Beginning."  My guess would be, with all the ships being destroyed during the war with the Minbari, mass production of new ships was necessary just to try and keep the Minbari attackers at bay.

From the time Earth became Jump capable in 2156 till the era of the the Earth/Minbari war 2245/48 , a minimal of some 60,000 capital scale vessels ranging from military cargo ships to the large scale Destroyers had come and gone.  Of these, some 70% had probably been disabled / destroyed during war, accidents, acts of god etc.  This high loss ratio is do in large part to Earth's war with the Minbari.

With a loss of 70% of the original 60,000, the Earth Alliance probably had a total of 18,000 ships.  Of the 18,000 strong fleet of the Earth Alliance, at least half of these are support vessels for the fleet - cutting us down to 9,000 vessels.  Of this figure, at least half are likely border patrol type vessels, corvettes etc.  This gives us a fleet strength of some 4,500 large-scale capital vessels, ranging from small Light Cruisers to large scale Destroyers.

As such Earth Alliance probably only has a viable combat fleet of 4,500 vessels, consisting of Destroyers, Carriers, Dreadnoughts, Battle Cruisers, Frigates, and Cruisers of varying sizes.

Given the volume of galactic space, this is not too liberal a figure when one considers that the United States Navy has a viable combat fleet of some 350 odd vessels, with about 4,000 aircraft in service.  This is just to serve the needs of a single nation on one planet, not a sprawling galactic empire spanning dozens of solar systems.

With a total of 35 planets and outposts under the dominion of the Earth Alliance, the Earth would be able to deploy 128 capital ships to defend her every territory.  Unfortunately, Earth also has defense pacts with other worlds and her fleet not only patrols Earth Alliance territories but the League World territories near their empire as well, just as the United States deploys her fleets to allied countries and patrol oceans far from the American border.

During the Earth Civil War, Earth Alliance's fleet was nearly cut in half, with some opting to join Captain Sheridan's forces, while the others remained loyal to President Clark.  This, in effect, would have cut Earth Alliance's fleet down to only 2,250 vessels, allowing them to deploy only 64 starships per. Earth Alliance territory.  Even more ships were lost, when either destroyed or captured by the forces of John Sheridan and his Whitestar fleet.  In addition to this, many Earth vessels did not participate in the war, opting to remain neutral rather than join the wrong side... which ever side that might be.

By the time Sheridan's forces would have gotten to Earth, less than 60 odd ships would have been there to defend that area, some smaller vessels stationed at Jupiter and Saturn, while a fleet of 30 to 35 Omega class Destroyers faced off against Sheridan's forces at Mars.  Sheridan's own forces were depleted due to his fleet having to sacrifice many a warship to maintain guard over the captured Earth vessels and crews loyal to Clark, as well as being forced to maintain a vigil over liberated Earth colonies and outposts.

All in all, at present, Earth likely has a fleet consisting of some 20,000 capital scale vessels.  Of these, roughly 900 to 1,400 likely fall into the Omega classification. Those who doubt this figure, please note that in the TNT movie "A Call to Arms" some 212 Omega class Destroyers were blown out of the night and, while a seizable number, this loss was not significant enough to cripple the whole of the Earth fleet; we know from Gideon's arrival that many ships were still in rout to Earth during the battle.

Also, much of Earth's fleet probably consists of smaller capital scale vessels built to support the primary war-fleet, or patrol the borders of Earth Alliance held territories and maintain a presence where Earth has a vital interest.  Its also not unthinkable to assume that as much as half of Earth Alliance's forces are in dry dock or mothballs, ready to be called back into active service should war again break out, just like the United States and other great Naval powers of the 20th / 21st centuries.