From the release:
Armies of the United States receive a boost this week with the outrageous-looking Calliope multiple rocket launcher!
Please note the pack contains 1 resin and metal rocket launcher – the tank is not included! The Calliope perfects fits all of our US Sherman variants (apart from the sandbagged version) so you can add it to an existing tank of pick up a new one to go with it.
All the rules for the Calliope can be found in the Bolt Action supplement Armies of the United States