Battery.

This is coolbert:

Battery SDV? SDV = Swimmer delivery vehicle. Combat swimmers of the naval commando type.

With regard to the two previous blog entries, SDV I and SDV II, consider how the range of such swimmer diver vehicles can be increased tenfold [10X] as described.

"Batteries that 'drink' seawater could power long-range underwater vehicles"

"Startup’s novel aluminum batteries increase the range of UUVs tenfold."

Not only UUV [unmanned undersea vehicles] but I can well imagine the S351 SDV also.

From https://news.mit.edu | Rob Matheson | MIT News Office |  June 15, 2017.

"Open Water Power’s battery that "drinks" in sea water to operate is safer and cheaper, and provides a tenfold increase in range, over traditional lithium-ion batteries used for unpiloted underwater vehicles. The power system consists of an alloyed aluminum anode, an alloyed cathode, and an alkaline electrolyte positioned between the electrodes. Components are only activated when flooded with water."

Increased SAFETY as well by several [?] magnitudes?

[....]

"Most UUVs use lithium-based batteries, which have several issues. They’re known to catch fire, for one thing, so UUV-sized batteries are generally not shippable by air. Also, their energy density is limited, meaning expensive service ships chaperone UUVs to sea, recharging the batteries as necessary."

Consider the announced range of the S351 SDV as: "a maximum range of 66 nautical miles ( 122 km ). Using this revolutionary battery can extend the range of a S351 to 660 NM or 750 standard miles.

What isn't there to like. To be honest it sounds almost too good to be true!

coolbert.