A trim vane assembly for amphibious armored vehicles and having a trim vane movable along a generally horizontal path between a deployed position in which the trim vane extends rearward from the vehicle and a stowed position in which the trim vane is positioned beneath the amphibious vehicle. In the retracted position, the trim vane movable is flush against or received within the vehicle bottom such that the trim vane supplements the belly armor. Similarly, the trim vane extends from or overlaps with the bottom of the vehicle when extended into the deployed position to provide continuous bottom face of the vehicle extending from the front of the vehicle to the end of the trim vane. Conventional trim vanes are rotated between a vertical orientation against the rear of the vehicle and a horizontal position extending from the rear of the vehicle reducing viscous drag.