Complex sentence: The Briggs Group became involved in the marine industry in the 1970s providing workboats to marine construction works and by the 1980s was providing vessels and manpower for Oil and Gas terminal operations across the UK.
Split into simpler sentences: The Briggs Group became involved in the marine industry in the 1970s, providing workboats to marine construction works. By the 1980s, it was providing vessels and manpower for oil and gas terminal operations across the UK.