 The armor of the M4 was effective against most early war tank and anti-tank weapons, but needed a compound angle to resist later German tank and anti-tank guns.The distinctive protruding "hatchways" of the early Sherman compromised the 56 degree-angled glacis plate, making them weak points where the effect of the glacis plate's slope was greatly reduced.In 1943, to make the thickness of these areas equal with the rest of the glacis plate, appliqué armor plates were fitted in front of them.