A high-velocity impact fragmentation of a polyethylene projectile and aluminium projectile on the steel mesh bumpers was investigated experimentally and numerically. The projectile velocity was about 3 km/s. The projectile destruction on mesh bumpers is especially distinguished by the accompanying formation of jets of fragments which are ejected from the front part of the projectile along and across its movement direction. The action of the jets on the witness plate (evaluated by the craters depth) can exceed the action of the remaining projectile mass. The numerical modelling evaluates the revealed cumulative effect as follows: the velocity of the fragments in the jets exceeds the original projectile velocity up to factor of ~1.5 in case when the projectile is aimed towards a cell centre. Numerical modelling also explains the mechanism of the formation of craters groups linearly distributed over the witness surface which were observed in the experiments on projectile fragmentation upon the mesh bumpers.