The merchant ships in the Duisburg convoy are listed in gross register tons. A register ton represents 100 cubic feet of internal space. It therefore measures a volume rather than the displacement of a ship. The term is linked to the wine tun, a barrel, explaining the similar words used for volume and weight. The similar wording can make comparisons misleading unless the type of tonnage is kept clear.
Notable Point · 5:01:43-5:03:00
Gross register tonnage measures internal volume
The convoy's GRT figures describe cargo-ship volume and cannot be read as warship displacement.