What is the rationale for the CH-53K? Could a navalized MH-47 do the job?

Honest question.

What is the rationale for the CH-53K?  How can the USMC justify the purchase of a helicopter that costs over 135 mil per copy?

Unless a case can be made that the CH-53K is absolutely essential and that a navalized MH-47 couldn't do the job (or at least most of the job) then how can it be justified?

I have yet to even read a justification for the numbers being sought (200).

Maybe the CH-53K is absolutely essential to future Marine Corps operations. Maybe only the CH-53K can meet the needs of the Marine Corps. But if we're going to ask the public to swallow a price tag that large then the case needs to be made why a unique platform is needed instead of going with a cheaper option modified to meet the needs of the Marine Corps.

Consider the following...

1.  The CH-47 comes from the factory sealed against dust and water.  Water landings are part of the certification (or were) process.

2.  Other forces use the CH-47 from amphibious ships.

3.  SOCOM/US Army CH-47s are frequent visitors to US Navy ships.

4.  From the outside looking in safety features for deck and aircrew would be the major modifications.  Folding rotors, corrosion resistance, mods to allow air crew passengers escape from the airplane over water and of course mods to its electronics.

In short it should be an engineering challenge, not a show stopper.

Just a reminder of why this is a burning issue.  Via Bloomberg....

Lockheed Marine Helicopter Came With Unpublicized Cost Increase
The Pentagon’s approval for the Marine Corps to start buying Lockheed Martin Corp.’s new heavy lift helicopter came with a hidden surprise: the projected total acquisition cost for the King Stallion program has increased 6.9 percent to $31 billion.

The updated estimate was provided in an April 4 decision memo by James MacStravic, the Pentagon’s acting weapons buyer, that authorized production of the initial batch of 26 helicopters. The memo, labeled “For Official Use Only,” was obtained by Bloomberg News.

The estimate for the total acquisition cost -- which includes everything from research to purchase of the aircraft, including spare parts -- climbed to $31 billion from about $29 billion that the Navy reported in March 2016. No aircraft were added beyond the 200 planned.

Likewise, the “program acquisition unit cost” estimate, with everything included, increased to $138.5 million per copter from $131.2 million as of August 2016. The latest projection is a 20 percent increase from the initial goal of about $115 million established in late 2005, according to data in the memo.

How much longer can the USMC be considered viable...how long will we be considered a value to the taxpayer with gear that costs this much?