Method and device for improving the inertial navigation of a vehicle

The method involves determining mean biases of accelerometers and gyrometers of an inertial unit (IM) of a craft (M) using an inertial unit (IL) of a carrier (L) before firing the craft from the carrier. Measurements of the accelerometers and the gyrometers output by the inertial unit of the craft are corrected by the mean biases determined before launching, where the inertial unit of the carrier and the inertial unit of the craft are provided with own reference axes (R-T, X-Z). An independent claim is also included for a device for improving inertial navigation of a machine.