hMG cupola casemate - may 1940
Typical profile of the very capable Dutch steel/concrete cupola casemate [called G-kazemat], suitable for a heavy machinegun.
The larger part of the casemate was hidden in the ground. The profile was extremely low and small and therefore hard to hit by adverse artillery. The concrete sides were capable of sustaining quite heavy impact and the 10 cm steel cupola was only vulnerable to 8,8 cm direct fire. All other German means were useless against the thick steel structure.
This particular casemate (in the picture) was quite rare by the way; the peculiar angle of the cupola was rarely seen [mind you: enemy position would be to the right of the picture, e.g. in a 90 degrees angle from the loop-hole. This 90 degree angle - with concrete protection from the main enemy fire-direction - was meant to be able to produce flanking fire, which was usually the mode in second line defences or when a casemate had to cover one or more other casemates against outflanking manoeuvres.