This series contains correspondence and documents relating to the Port Line administration. This includes earlier and subsidiary companies. Contents of this series include carbons of cables to and from ships and the line's agents and offices abroad, letters, newspaper clippings, and intelligence reports, notes of interviews and copies of minutes of official bodies. The subjects deal with the Port Line's business trading with Australia and New Zealand.

Managers and directors sending or receiving correspondence include W. Donald, J. R. Rooper, R. H. Senior, W. de Gruchy and W. P. Tyser. Official bodies referred to include the Australian Tonnage Committee and the New Zealand Tonnage Committee, Ocean Shipowners' Group Joint Committee, the National Dock Labour Board, and the Waterfront Control Commission. Companies include Blue Star and the Montreal, Australia and New Zealand Line (MANZ).

The files in this series also relate to the D42/PL4 series as initially all files were stored together with some later being extracted by the company as part of a records management exercise in separating current and non-current material. Further files relating to this sequence can be found at D42/PL8/4