This naval fort was situated approx. 1100 meters east of the battery Quinti Bastion, and was built in the period 1860-1863 at approx. 3 meters water depth.
Towards the sea side the fort was bounded by a row of pillars in front of which was placed an approx. 1.5 m thick stone glaze. Above this is a 3-5 meter high and 2 meter thick concrete wall covered with granite. Towards the harbor was a concrete quay wall.
The fort had an approx. 90 meters long and approx. 25 meters deep front, two flanks at 35 and 25 meters depth as well as a northern harbor pier of 90 meters length and a southern pier of 40 meters.
The harbor within the pier was filled in the northern half. Here was barracks for 180 men built of 0.60 m thick concrete walls. The front wall was 6 feet thick and had an inner wall of 1.8 meters of concrete. At the front there was 1 middle traverses and two shoulder crossers. In here were built in ammunition magazines covered with 9 meters of concrete and 1-2 meters of earth.
The fort was armed with:
2 pcs. of 35.5 cm. steel cannon L / 30 on each flank
4 pcs. of 24 cm. steel cannon L / 40 with shields mounted on the face
3 pcs. of 47 mm. quick-firing steel cannon with shields, set up with 1 on the outer edge of each flank and 1 on
the northern shoulder traverse.
2 pcs. of 8 mm. 2-course mitrailleuse.
1 90 cm. floodlight.
The crew was in 1911 130 men. This was later increased to 170.
The Mellemfort has completely disappeared.