[a3n]

> How would they enforce security?

Make them submarines?

[femto]

Might that also lead to reduced stresses on the vessel, and less chance of something breaking? A failure might mean the whole lot ending up on the bottom of the sea?

[nradov]

You missed the joke. It's obviously not economically viable to build huge cargo submarines.

[protomyth]

The Russians were thinking about doing just that with their SSBN sub design. It didn't come to anything, but people have been doing the research in a serious manner.