One of the Starfleet vessels in the fleet Picard assembles on the Klingon-Romulan border during the Klingon Civil War to expose Romulan supply convoys with a tachyon detection grid.
The USS Akagi is named in the Next Generation episode Redemption II. With the House of Duras secretly supplied by the Romulans, Picard persuades Starfleet to let him form a blockade of some twenty ships along the border, linked by tachyon beams that will show up any cloaked vessel trying to cross.
The Akagi is one of the ships holding a place in the net. When Sela floods part of the grid with tachyons to open a gap around Data's ship, the USS Sutherland, Picard orders the fleet, the Akagi included, to fall back and re-form the net further along.
Data's refusal to follow that order exposes the Romulan convoy. The Akagi itself is only heard in dialogue and shown as a marker on the tactical display.