At the beginning of the Dominion War Starfleet was in a desperate situation to replace combat losses.
In one short-term solution, available components from multiple production series were combined and assembled together to shorten the construction time for new cruisers. The Diomede Medium Cruiser was the result of the combination of Intrepid saucer sections and mothballed Constitution parts, mainly warp nacelles and engineering hulls. The phaser banks and shield systems were slightly improved, but unfortunately the hull could only employ the standard Photon Torpedo tubes.
Only a few Diomedes were constructed and the few survivors were mostly mothballed in the decade after the war.