Back then many cargoes were shipped in barrels or smaller kegs. Here is the end of a small wooden keg, along with some staves. I can make out the word "WHIT(E)". The vessel's cargo included small barrels of cheese, which survives to this day as a foul-smelling white goo if you are unlucky enough to find any!
Surprisingly, of all the devices that make up an underwater diving kit, the last to be developed was a suitable air reservoir. Demand air valves ( regulators to you and me, ) masks, fins, snorkels, weights, even drysuits may be found in the historical record up to several hundred years ago, but because of material and manufacturing requirements, the high-capacity high-pressure portable air cylinder is a relatively recent development. ( Jacques Cousteau often gets credit for something he did not invent - the demand-valve regulator predates him considerably, although he did much to perfect its application to diving. )
Litigation has caused manufacturers to leave the market, and be replaced by others, who then left, and then others come back. From year to year, there's no telling what brand of tanks may be available, but the specs and recommendations below should apply to any.
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