Optimizing the routes of firefighting aircraft can lead to better containment of wildfires, hence yielding great environmental and societal value. In this paper, a novel formulation of the Vehicle Routing Problem (VRP) is customized to address the needs of Aerial FireFighting (AFF). The resulting formulation, named Aerial FireFighting Vehicle Routing Problem (AFFVRP), is a capacitated multi-trip VRP with time-windows and hierarchical objectives. The primary objective is to minimize the time of carrying out all requested water drops (to extinguish wildfires quicker), and the secondary objective is to minimize the total flight time. The multi-trip nuance is adopted to be able to model different aircraft types that might require to revisit the depot for after refueling. Because the model is intended to operate as a decision-making tool to support firefighters, users can input the number and types of aircraft available, the location of the airfield, fires, nearest water body, intensity of each fire, etc. Several random cases and case studied based on real wildfires were solved within the expert-recommended time limit of 5 minutes, yielding good-quality solutions in terms of gap optimality. The problem is scalable and sizes ranging from one to 80 water drops were tested and solved within 22 minutes. Strategic fleet planning is also demonstrated in a case study with the use of Monte Carlo simulation, in order to compare the performance of different fleet options for a given setting. Therefore, the model is not only applicable in live situations, but can also be used as a supportive tool in planning for upcoming fire seasons, or reviewing and learning from past fires.