Complex sentence: ML contracted Cammell Laird of Birkenhead to build two smaller vessels of 1,800 tons and these were commissioned in 1952, named the "Manchester Pioneer" and "Explorer".
Split into simpler sentences: ML contracted Cammell Laird of Birkenhead to build two smaller vessels of 1,800 tons. Commissioned in 1952, they were named the "Manchester Pioneer" and "Explorer".