Common Support Ship

The military has been pursuing commonality and modularity for some time, now, and with generally dismal results.  In particular, the military has been fascinated with the idea of common platforms that can be modified to serve multiple functions.

The Army has attempted to create a common vehicle, both armored and non, from which families of specialized vehicles can be created.  The Stryker and Bradley have both been used as the basis for multiple, specialized vehicles with some degree of success.

The various aviation services have attempted to create common airframes.  The F-35 is an example of such an attempt.  The S-3 Viking, though not an intentional attempt at a common airframe, did develop into ASW, SigInt, Tanker, and COD airframes.

The Navy attempted to create a base LCS that could morph into specialized functions via swappable modules – a disaster on every level.  The Navy also appears to be attempting to use the San Antonia LPD as a common hull, necking down various amphibious ship types, replacing older LPDs and LSD-41/49s.  It has also been proposed as a dedicated ballistic missile defense ship.

And so on.

Most attempts at a common base have met with limited success for a variety of reasons.  Ironically, the example of the unintended common airframe of the S-3 Viking has, arguably, met with the greatest success.

Along the lines of a common airframe, one could imagine a common hull for a range of support ships.  A reader offered this idea in a comment in a previous post and suggested uses such as mobile HQ's, hospital ships, mother ships, ammunition haulers, artillery/rocket platforms, and repair shops. (1)

ComNavOps has stated repeatedly that modularity is, by definition, a sub-optimal solution – a failure, in essence.  So, why would a common hull be a good idea?  The difference is the application.  Commonality and modularity are failures for combat platforms because, as I said, they inherently produce sub-optimal platforms and sub-optimal platforms will lose to optimized platforms every time.  On the other hand, for non-combat applications, like a family of support ships, the fact that they aren’t exquisitely optimized really doesn’t matter.  A little inefficiency in a support role is perfectly acceptable.

What we’re talking about with a common hull is, basically, a WWII Liberty ship.  A fairly generic ship that can be quickly and cheaply produced and can, with minimal modifications, serve a variety of functions.

The danger in trying to adopt a common support hull is making it too all-encompassing.  The hull size required to support an EOD MCM unit is much smaller than that required for hospital ship.  If one sizes the common hull for the largest possible application then all the lesser applications wind up with a ship that is too big and, as a consequence, overpriced.  Thus, for a common support hull to work we have to limit the applications to those that share a reasonably similar area (square) and volumetric (cube) need.

Here’s a list of possible functions that could be accomplished with a common hull and the required vessel size.

mobile HQ's – small

repair vessel - small

tender - medium

artillery/rocket platforms – medium
MCM mother ship – medium

troop transport - large

hospital ships - large
ammunition haulers – large

We see, then, that we need three different size ‘common’ vessels to meet our family of needs.  To stretch our Liberty ship example, we would need three different size Liberty vessels.  They could share common characteristics (length to beam ratio, etc.), I suppose, but at some point you’ve got to face the fact that you’ve designed a different ship for each vessel group size.  There’s nothing wrong with that.  Having three ‘classes’ of common ship would be fine.  It might even be possible to condense the three sizes into two without imposing too much waste and inefficiency.  I’ll leave that up to the designers.

The larger point is that there’s a fine line between commonality cost savings and operational inefficiencies due to the non-optimized commonality.  For example, in our medium size group, an MCM mothership would likely need a radically different stern structure for unmanned vehicle launches, small boat launches, etc. than a tender or artillery/rocket platform ship.  Yes, you can take the common medium hull and greatly modify it to fit the MCM mothership requirements but after you do, you’ve probably lost any cost savings that came from the original commonality.  Is it worth it or is it better to just design a different, optimized mothership?  I’m not offering an answer to that, just illustrating the challenge of assessing the balance between commonality and optimization.

So, there is certainly some potential for a common support hull – or maybe two or three common support hull sizes – but we need to assess and balance the potential commonality cost savings against the non-optimized operational inefficiencies.

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(1)Navy Matters, “LST Development and Death”, 25-Mar-2019, comment: Seal Of Lion, March 25, 2019 at 8:03 PM,

https://navy-matters.blogspot.com/2019/03/lst-development-and-death.html?showComment=1553614885463#c825706147726727874