by John Marshall, Royal Naval Biography — Steuart… (1823)
“ The “stone expedition” here attracts our attention. This was an expedient proposed to block up the harbour of Boulogne, by sinking ships, loaded with stones, at its entrance; and to effect which, three merchant-vessels, of about 400 tons each, were purchased, and their holds filled with blocks of granite, well cemented and clamped together, so as to resist the action of the sea, at least for a certain time: this part of the preparation being complete, the vessels were next rendered combustible, by the addition of every thing inflammatory that could be laid in them. ”
