Commanders can intercept Royal Shipments or an Unit Express with their armies when actively spinning in PvP. Royal Shipments contain a valuable mixture of different items. A Unit Express contains a valuable assortment of Unit Shards and resources.
When a player encounters a Royal Shipment, or a Unit Express they can decide whether they want to claim the shipment or leave it be.
Some Royal Shipments can be claimed for free, others require you to watch an ad and some Royal Shipments cost Gems or real money. All Unit Express offers involve a real money purchase.