AbstractIt has long been assumed that the planet Jupiter acts as a giant shield, significantly lowering the impact rate of minor bodies on Earth. However, until recently, very little work had been carried out examining the role played by Jupiter in determining the frequency of such collisions. In this work, the third of a series of papers, we examine the degree to which the impact rate on Earth resulting from the Oort cloud comets is enhanced or lessened by the presence of a giant planet in a Jupiter-like orbit, in an attempt to more fully understand the impact regime under which life on Earth has developed. Our results show that the presence of a giant planet in a Jupiter-like orbit significantly alters the impact rate of Oort cloud comets on Earth, decreasing the rate as the mass of the giant planet increases. The greatest bombardment flux is observed when no giant planet is present.