With this upgrade, husks from heavy units will regain health over time. When the husk is at full HP, the unit comes back online at 50% HP. Husks can be destroyed or captured before this happens so they must be protected.
It is important to note that this upgrade comes from the Offense Class. And can therefore only be applied to the Rhino and Aftershock, which are both Defense units, if the player switches to the offense class to buy the upgrade, after he or she has unlocked tier 3 tech on his or her Defense Crawler.