Complex sentence: In 1982 she was docked at Tilbury, and in June 1999 "Belfast" was towed to Portsmouth, the first time she had been to sea in 28 years; a Certificate of Seaworthiness had to be obtained from the Maritime and Coastguard Agency.
Split into simpler sentences: In 1982 she was docked at Tilbury, and in June 1999 "Belfast" was towed to Portsmouth. This was the first time she had been to sea in 28 years and required a Certificate of Seaworthiness from the Maritime and Coastguard Agency.