Disadvantages of the vehicle included a low rate of fire due to the heavy ammunition, low ammunition storage (only 20 rounds) and a cramped and un-ergonomic crew compartment. Its armor protection was only adequate; the 65 mm of 30-degree sloped frontal armor still left it vulnerable frontally to the 88 mm KwK 36/43 guns of the Tiger and Ferdinand/Elefant at long range and the 7.5 cm KwK 40 high-velocity gun of the Panzer IV and StuG III/IV at medium and short ranges (and from any range from the flanks or rear). The 152 mm gun, while having a maximum range far superior to the 88 mm, was still a corps-level heavy howitzer at heart, and had a much shorter accurate range than either the 88 mm or the 7.5 cm gun while still being vulnerable to return fire at the same distance. This made it most effective for use in massed ambushes, where the German heavy tanks' advantages could be nullified and the SU-152's one-shot kill potential could be best utilized.