The original production run. Entering commission 20 years after the end of the Cylon war, and representing a revolutionary shift in the design of colonial warship, the Mercury's were the most powerful warships ever created.
The Block 0 was the first production class of battlestar to feature non-retracting pods. Physically they were distinct from latter examples due to the completely overlapping flight pods. This also meant that they carried a smaller air-wing and had worse arcs of fire, but did provide greater structural soundness.
Eventually the entire block underwent a massive refit that greatly improved the offensive capacity and saw many used to test experimental systems. The refit included the addition of spine mounted cannons and heavy missiles, both additions that would be incorporated in the Block II.
At the time of the second cylon war the Block 0's were being phased out and replaced with Block II's and in the case of the Atlantia, the Nova Class.