Everything is lost. Not even dog tags that have been earned are retained. Every weapon and module needs to be unlocked and leveled yet again. It would have been nice if some of the experience earned could have been retained, like perhaps module levels, but nope. Not to mention those excruciating first dozen levels; all the starting weapons get crushed by their higher level brethren.
Apparently this goes on another 4 times and the only thing earned each time is an extra dog tag? That might be fine for some, but I'll likely pass. I'll take the unlocks over the extra badges and pride.