Satsuma,
OK - let's bat off the insults. There's a number of simple reasons why a marinised CH-47 doesn't exist.
1. Money. It's not a simple feat to marinise an airframe that wasn't designed for it. At all. SABR would have fitted folding heads, bespoke naval kit and "wet" constructed the airframes. All of which costs a massive amount of money. If we only bought 15-20 you'd have to amortise the R&D over a pitifully small number of airframes bumping the unit cost up to a ridiculous amount unless you could convince other nations to buy it.
2. V-22. Boeing were not really interested in marinising the Chinook as there was always a fear it would do massive damage to export opportunities for the V-22.
3. USMC. They love Stallions and they were not going to change to a -47 based design. Hence the $Bns spent on the -53K which, at the last time I looked, had an estimated unit cost of $120M vice a CH-47F at $40m. See point one about money over small production runs......
I'm an ex-47 driver, I've flown off carriers and completed the RM Amphib Ops Planning Course. Without going into detail there are several good reasons why you don't want a single type in your TAG. A combination of Merlin and Chinook will serve the RM well - the Chinooks only embarking for exercises and Ops leaving the CHF to float around the world on a full time basis. You need the grunt of the Chinook for the heavier combat configured loads and, yes, you can do a double company lift with about a third the number of CH47s as Merlins but there are sometimes sound military reasons why you don't want to do that.
The answer to nearly every question that can be posed is "two chinooks" (joke!) but the Littoral is one area where the nuances suit a TAG much better. Plus, with Me4 embarked on a Phib or the CVF, if it kicks off the other side of the world and the ship is nearby, you're not going to get Chinooks there in a hurry.......