Complex sentence: These are large reinforced buried concrete bunkers, equipped with armoured turrets containing high-precision optics that were connected with the other fortifications by field telephone and wireless transmitters (known in French by the acronym T.S.F.).
Split into simpler sentences: These are large reinforced buried concrete bunkers, equipped with armoured turrets with high-precision optics. They were connected to the other fortifications by field telephone and wireless transmitters (known in French by the acronym T.S.F.).