[topher]

Oops!

Should have been:

There is a simple and quick fix: ATTACH a 2 inch thick steel plate (or thicker) about 4 feet below the bottom of the tanker...

[WhoisAlanGreenspan?]

I'm guessing you're on the right track; submarine ramming attempt on the prop. See post 15 for larger pic.

But I'd also suppose the best defence against submarine rammings in the middle of the night would be a navy destroyer escort. I think the message is 'you've been warned'.