New ship for the US Navy

The Expeditionary Sea Base ship, USNS Miguel Keith, successfully completed its acceptance trials off the California coast, the U.S. Navy announced:


Can anybody explain why build a semi-submersible transport vessel and then fill the deck with a large structure that is obviously not buoyant, or easily removable??
What is that large submersible deck used for?

Purely supposition on my part but the submersible deck can handle the navy’s LCAC (Landing Craft Air Cushion) and similar craft while simultaneously allowing helio operations on the upper deck.

More info here:
https://www.navsea.navy.mil/Home/Team-Ships/PEO-Ships/Exp-Transfer-Dock-ESD-Exp-Sea-Base-ESB/

Thanks. That sound logical, although it appears to have been an afterthought, not part of the original design, or planned operation.
The ships were designed to submerge the deck to float fairly large and deep draft vessels or floating units on/off. Those LCACs just need the deck to be level with the sea surface, I believe(??)

Both MLP and AFSB(later to become ESD and ESB) ships were never designed to actually submerge the “well deck” and float on any vessel other than the LCAC. Some of the concept testing did include use of semi-sub vessel, but this was strictly to test the feasibility of the MLP operation. The semi sub vessel was the only ship that could provide a deck area suitable for the test. These tests focused on using a bridge ramp module to stage vehicles on the deck of a Semi Sub. I spent a few years on the AFSB test platform and over that time some of the MPL and AFSB design renderings and eventually the final plans were shown to us. The MLP concept has always been skin to skin transfer of vehicles via portable ramp module. Offloaded vehicles would discharge to the deck of the MLP and then stage for embarkation to LCAC. The USMC assets aboard the LCAC would then do their thing and hit the beach.
more info:the sraight dope
as well as:https://en.wikipedia.org/wiki/Expeditionary_Transfer_Dock

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It is a pity that the acceptance trials didn’t include photos of the ship (actually a tanker) being submerged, so the mobile landing platform on top could free float on its own, sail away and anchor somewhere else. Can the mobile landing platform later be recovered by the mother ship and brought to another war location?

The original design looks like it was modeled on the American Cormorant, which was originally the crude oil tanker Kollbrise, built in Sweden in 1975 and converted to the semi-submersible HLV Ferncarrier in 1982. She was sold to the US Navy in 1985 and operated mainly as a forward base at Diego Garcia:
image
She was sold in 2005 and became HLV Asian Atlas, until scrapped in 2014.

The first two of this type built for US Navy was originally very similar, until the third was delivered as an ESD, with the raised deck and very different purpose.

BTW; it doesn’t look like MARAD know much about the American Comorent:
https://vesselhistory.marad.dot.gov/ShipHistory/Detail/6662
(Or maybe it is Top Secret??)

The entire vessel is the “Mobile Landing Platform” there is no “separate part” to float off.

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It is a mobile special operations base. They can park it offshore packed with helo’s, fast boats, and SEALS. Then do what they do best.

I passed this thing while it was in the shipyard. The forward structure is enormous and almost completely blocks the sight line of the after house where the bridge is. I’m guessing they plan on navigating by instruments and damned be whomever gets in their way.

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Yes that is obviously true of the present configuration, but why than build them to submerge to several meters above deck?
Not sure how many meters, but Ferncarrier was able to “dive” to 7.5 m. above deck, I believe.

As for the navigation aspect, that is probably not a major concern in the “repurposing” of these vessels. (Nobody look out the windows these days anyhow)

It’s not designed to submerge. The earliest Montford Point class ships were designed to submerge. The later versions with the midship flight deck are not submerciable.

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Yes, It certainly does look like the old Cormorat MLP was never inteded to re-boot the mission that the Cormorant supported. The MLP change in draft to support LCAC is minimal and that is where the story ends. If you read the links I posted you can see the US GOV and NASSCO essentially took the Alaska Class tanker platform, shortened it by 100ft and nothed out the deck as a cost cutting measure in order to get the operational capability they desired. The USN probably saved the taxpayer a few billion by using an esting design and modfying it, instead of designing and building a completely new class of vessel.

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It looks like the mobile platform is carried on the main deck to be off-loaded and floated away when the ship is submerged.

That picture is of either the first or second ship in the class. Those were initially intended to submerge. The later ones have large flight decks above the main deck. Those decks are not removable and the ships do not submerge.

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The photo already posted, the one with teh flat empty deck, was taken from the sea trials before the wells for 3 LCAC and a vehicle staging area were added. There is a LOT more to the MPL than is shown in this photo. THIS IS NOT WHAT THE SHIP LOOKED LIKE WHEN IT WAS DELIVERED TO MSC.

USNS-Montford-Point03

This as far as she goes down, in no way a true semi-sub like the Marlin ships or the Cormorant. You can clearly see the vehicle staging area(above the waterline)

mic drop?

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An Expeditionary Transfer Dock (ESD) , formerly the Mobile Landing Platform (MLP), and a sub-class variant; the Expeditionary Mobile Base (ESB) (topic), formerly the Afloat Forward Staging Base (AFSB), are designed to be a semi-submersible, flexible, modular platform providing the US Navy with the capability to perform large-scale logistics movements such as the transfer of vehicles and equipment from sea to shore. These ships significantly reduce the dependency on foreign ports and provide support in the absence of port availability, we are told by USN.
How this semi-submersible ship/tanker can transfer vehicles and equipment from sea to shore remains a mystery to me.

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Topic is this ESB USNS Miguel Keith that can transfer vehicles and equipment from sea to shore in war. But LCACs? I see from photo above/below that three LCACs are stored below(!) the mobile platform, half of which is removed before LCACs launching.
image

I have to admit I do not understand how this half submerged ESB is supposed to work at sea. Speed is 0. Three LCACs are launched to starboard. OK, on port side is a ramp … for what? And the mobile top deck is empty.

Yeah I see your point. Looks like the ESDs have the LCACs not the ESBs. From here:

https://www.navsea.navy.mil/Home/Team-Ships/PEO-Ships/Exp-Transfer-Dock-ESD-Exp-Sea-Base-ESB/

“ESBs include a four spot flight deck, mission deck and hangar, are designed around four core capabilities: aviation facilities, berthing, equipment staging support, and command and control assets.”

Whereas the ESDs:

“The USNS Montford Point (T-ESD 1) and USNS John Glenn (T-ESD 2) are configured with the Core Capability Set (CCS), which consists of a vehicle staging area, vehicle transfer ramp, large mooring fenders and up to three Landing Craft Air Cushion (LCAC) vessel lanes to support its core equipment transfer requirements.”

It appears that your mystery is solved…the ESBs will not transfer vehicles and equipment from sea to shore. The ESDs will take care of that.

Ok, the ESD has three LCACs on the main deck below the mobile platform deck, the ESD is submerged and heeled and the emplty LCACs take off to hit the enemy.
But what about ESB USNS Miguel Keith. Is it submersible?

Doesn’t appear to be. It appears to focus on other missions as detailed in that link.