Though the M26 Pershing brought a new level of firepower and protection for American tankers in the late end of World War II in Europe, there was a perceived need for additional firepower to be attached to the vehicle. Perhaps inspired by the Calliope based on the M4 Sherman, the M26 upgrade was done by attaching T99 rocket launcher pods on both sides of the turret that could hold a total of 44 rockets. This modified M26 was tested at Aberdeen around December 1945, after the conclusion of World War II. With not much mention of the tank after this testing period, the M26 with T99 launchers was presumably caught up in the post-war military budget cuts and cancelled.

The M26 T99 is a premium tank introduced into War Thunder in Update 1.53 "Firestorm". The vehicle is essentially a M26 Pershing tank equipped with rocket pods on both sides of the turret. With a total of 44 M8 rockets, players have more firepower options aside from the 90 mm M3 gun, allowing for quick follow-up attacks while the 90 mm reloads.