The present invention describes a process for the production of fuel of the heavy fuel oil type, this fuel optionally being able to become a marine fuel, from a heavy hydrocarbon-containing feedstock having a sulphur content of at least 0.5% by weight, an initial boiling temperature of at least 350° C. and a final boiling temperature of at least 450° C., a process using a fixed-bed hydrotreatment stage, an intermediate separation and a hydrocracking stage comprising at least one reactor of the hybrid type.