The machine-gun casemates were coated by 4-layer armoured plates. The plates were fixed on the lateral concrete basis by stay-bolts. These plates were taken from Russian Fort Ino which was ruined in 1920th. The narrow embrasures were notched in the plates. Such construction provided more low silhouette of installation. Early in the February, 1940 casemates of Ink-6 were under direct fire of Soviet artillery of big caliber (up to 152 mm). Two outer layer of the plates were cracked, but pillbox survived and preserved its efficiency.