The Grimmershörn Fortress was a semi-open field redoubt, the main front of which ran parallel to the dyke. Its entrance was an open cut in the valley wall with a full and lattice gate. The dimensions of the structure were 175 m long along the front, 82 m deep along the left flank and 60 m deep along the right flank. The left flank and the left part of the front bedding were designed for medium-caliber guns in ship casemates. The hollow shoulder defenses served as projectile and cartridge rooms and to accommodate the ammunition conveyor systems. Open platoon commander's positions were located between each two casemates, and two further splinter-proof commander's positions were in the middle of the battery on the hollow shoulder defenses. The valley wall of the fort was expanded to provide infantry defense against attacks. In the redoubt there were corresponding hollow spaces under the main wall and at the left shoulder point. There were three guard and standby rooms, 4 storeys and cartridge rooms, an engine room and an accumulator room. The telephone exchange was located in the left gate casemate, and the telegraph room and switching center of the battery were in the right gate casemate.

During the Second World War, the old "Fort Grimmershörn" continued to be used for coastal defense against enemy ship attacks. It was armed with four quick-loading cannons model 10.5 cm SK/C 32 U, as used on German submarines, and there was also a light infantry gun 7.62 IKH 290. To protect against approaching low-flying aircraft, there was at least one 2 cm Flak 29 Oerlikon on a pedestal mount 40.