Saphroneth
Banned
Alternatively, just fill the Channel with rubble.
It is only 30 km wide x 30 m deep on average. Making a reasonable causeway across requires only a realistic amount of rubble.
Hey, for only twice the amount of rubble, you could even polderize a whole section of Channel! Makes it easier to drag artillery (and horses) across.
You could even use the before-mentioned trebuchet to throw these stones into place. Let the perfidious Albion try to defend against this!
A realistic amount of rubble meaning that, for a 10 m wide causeway, you need...
9 million cumecs. In other words, for a perfectly smooth-sided causeway, you need approx. the volume of concrete in the Hoover dam per 2.5 metres wide.
Angle of repose for rubble is, what, 30 degrees...
Call it a "down payment" of about 10 million cumecs as the underwater sloping sides, plus 1 million cumec per metre of width.
This is actually surprisingly doable (relatively speaking), so long as you ignore little things like weather, tides or waves. It's like a photonegative Suez.