The Tempest class refit will be improved to include a fifth tactical console slot, better bridge officer seating, and increased aft firepower. It'll also come standard with a Nadion Saturation Bomb console that "lays down a string of explosive fire" to the enemy ship and beyond, leaving a damaging radiation field afterward. The ship will require Vice Admiral rank and 2,500 ZEN to purchase.
The Maelstrom class refit isn't as grand due to its size, but it will be beefed up, add a third engineering console slot, and include a fused aft Tempest tail gun. This ship also requires Vice Admiral rank to purchase along with five fleet modules.