For context, the contemporary commercial merchant fleet is about 80,000 ships, roughly a third of which are bulk liquid carriers (a/k/a oil tankers). As a percentage, that's actually down from the 1970s/80s when <i>half</i> of all commercial ships were tankers. Most of the growth has been in container ships.<p>Relevant to WWII, oil tanker losses by the US alone were staggering. "A total of 129 tankers were lost in American waters in the first five months of 1942." (<<a href="https://warfarehistorynetwork.com/article/operation-drumbeats-devastating-toll-on-allied-shipping/" rel="nofollow">https://warfarehistorynetwork.com/article/operation-drumbeat...</a>>).<p>A consequence was the US government building the first long-distance oil pipelines, the "Big Inch" and "Little Big Inch" pipelines from east Texas to refineries on the Atlantic seaboard in New Jersey. They remain in use.<p><<a href="https://en.wikipedia.org/wiki/Big_Inch" rel="nofollow">https://en.wikipedia.org/wiki/Big_Inch</a>><p>I've also realised that both whales and large-scale commercial shipping rely on similar circumstances: the ability to on- and off-board cargo (or food) rapidly, widely-separated ports (or feeding grounds), and no significant predators (or war / piracy hazards). Whales are a remarkably recent evolutionary development, with the large great whales dating back only about 5 million years. Similarly, bulk shipping required not only global markets but cargos which could be handled in aggregate, whether liquids (as with petroleum), dry solids (mostly ores), or containerised miscellaneous cargo, the latter being premised on standardisation. Canals, safe shipping routes, and quayside cargo handling capacity were also prerequisites.