Of the weapons of the Lutheran Triad, the Greymourn grenade launcher has the potential to be a devastating support weapon. However, its bulky ammunition is hard to load at the optimum rate possible without help. Therefore, Greymourns are often fielded with assistant Loaders to help carry extra ammunition and to load it on the battlefield.
By spending a full Turn (all three Actions) helping to load the Greymourn, the Loader gives the Greymourn operator +1 RC attack with the Greymourn grenade launcher this Turn. In order to get this bonus, the Loader must be activated before the Greymourn operator, and the Loader must be within 3" of the Greymourn.
Should a Greymourn be killed, and should the Loader be within 3" of the Greymourn model at the time, you may swap the models, and the Loader now becomes the Greymourn operator. Should the former Greymourn operator return to play (such as being healed by a Medic), it will act as the new Loader.