Action Packs are designed to have an extremely fast flash duration. They freeze fast moving action better than any other brand of high power flash system because they have a faster t0.1 time till the flash duration is finished.
The 400ws Action Pack has its fastest setting at its highest power, so 400ws is finished in 1/1500 second. It also has settings at 200ws and 100ws but they are slower.
The Pack has a seven light battery gauge and powers one Lumedyne Flash Head (Quartz Flashtube recommended) and it does give you the option of fast or extra fast recycling between flashes.